2021年1月23日发(作者：和柱)
Listening and Note-taking
Sleep
It
’
s
clear
that
everyone
needs
to sleep.
Most
people
rarely
think
about
how
or why
they sleep,
however. We know that if we sleep well we feel rested.
If we don
’
t sleep enough, we often feel
tired
and
irritable.
It seems
that
there
are
two
purposes
of
sleep:
physical
rest
and
emotional
or
psychological rest. We need to rest our bodies and our minds. Both are important in order for us to
be healthy.
Each night we alternate between two kinds of sleep: active sleep and passive sleep. The passive
sleep gives our body the rest that is needed and prepares us for active sleep
in which dreaming
occurs. And we are beginning to understand the importance of the dream stage in our sleep cycles.
Let
’
s look at the different kinds of sleep.
They
’
re quite different. In passive sleep, the body is at
rest. The heart slows down.
The body processes become very slow.
We move very little.
And the
brain becomes very inactive.
This stage of sleep is known as slow-wave sleep because the brain
waves move in a very slow regular rhythm.
If a person continues to sleep, she or he enters a new stage, a more active stage.
The body goes
through several changes: the brain temperature rises, the amount of blood in the brain increases,
the body becomes very
, very still, and the brain goes from being very inactive to being active. And
as the brain becomes more active, the eyes begin to move rapidly.
When the eyes begin to move,
this is a sign of another change
—
the change is that the person is dreaming.
Throughout the night, people alternate between passive and active sleep.
The brain rests, then it
becomes
active,
then
dreaming
occurs.
The
cycle
is
repeated:
the
brain
rests,
then
it
becomes
active,
then
dreaming
occurs.
This cycle
is repeated
several
times
throughout
the
night.
During
eight hours of sleep people dream for a total of one and a half hours, on the average.
All people experience these dream cycles.
Many people say they don
’
t dream, or that they rarely
dream. Doctors have studied the sleep cycle and have found that everyone dreams
—
in fact, that
everyone needs to dream in order to stay healthy. It appears we need both kinds of sleep. We need
passive sleep in order to rest our bodies.
We need active sleep
in order to dream.
And dreaming
helps us to rest our minds.
Passage 1 what is a black hole?
A
black hole is a region of spacetime from which nothing can escape, even light.
To see why this
happens,
imagine
throwing
a
tennis
ball
into
the
air.
The
harder
you
throw
the
tennis
ball,
the
faster it is traveling when it leaves you hand and the higher the ball will go before turning back. If
you throw it hard enough it will never return; the gravitational attraction will not be able to pull it
back down. The velocity the ball must have to escape is known as
the escape velocity and for the
earth is about 7miles a second.
As a body is crushed into a smaller and smaller volume, the gravitational attraction increases, and
hence
the
escape
velocity
gets
bigger.
Things
have
to
be
thrown
harder
and
harder
to
escape.
Eventually a point is reached when even light, which travels at 186 thousand miles a second, is not
traveling fast enough to escape. At this point, nothing can get out as nothing can travel faster than
light. This is a black hole.
It is impossible to see a black hole directly because no light can escape from them; they are black.
But there are good reasons to think they exist.
When
a
large
star
has
been
built
all
its
fuel
it
explodes
into
a
supernova.
The
stuff
that
is
left
collapses down to an extremely dense object known as a neutron star.
We know that these
objects
exist because several have been found using radio telescopes.
If
the
neutron
star
is
too
large,
the
gravitational
forces
overwhelm
the
pressure
gradients
and
collapse
cannot
be
halted.
The
neutron star continues
to
shrink
until
it
finally
becomes
a
black
hole. This mass limit is only a couple of solar masses, that is about twice the mass of our sun, and
so we should expect at least a few neutron stars to have this mass. Our sun is not particularly large;
in fact it is quite small.
A

supernova
occurs
in
our
galaxy
once
every
300
years,
and
in
neighboring
galaxies
about
500
neutron stars have been identified. Therefore we are quite confident that there should also be some
black holes.
Passage 2 My Ancestor Was a Rhinoceros
At
one
time
I
thought
my
family
was
very
different
from
every
other family
in
the
world.
It
happened
because
I
had
trouble
with
a
word.
That word was
ancestor.
Today, I
know what
it
means. An ancestor is someone, a man or woman, in your family. That person is now dead, and
died many years, even hundreds of years, ago.
I first heard the word in a story my mother told me one night.
“
what,
”
I asked her,
“
is an ancestor?
”

My mother never made things easy for me. She went to a box and brought out a photograph.
“
That,
”
she said,
“
is your ancestor.
”

I looked at the photograph. Lying on the ground was a large animal.
It had two small eyes, a big
white horn on its nose, and a small tail. The animal was not asleep, I was sure of that. It was dead.
So ,that was my ancestor. I went to sleep and dreamt of large animals.
The next day I went to my mother and said,
“
Are ancestors always dead?
”

“
Oh, yes,
”
she told me.
“
They have to be dead. Y
ou can
’
t have a live ancestor.
”

“
Only dead ones?
”

“
Y
es.
”

Some days later I went to a friend
’
s house.
“
Have you got any photographs of your ancestors?
”
I
asked.

“
Lots
,”
he said.
“
Can I see?
”

His ancestors were different.
His ancestors were all people.
Men and women. I felt very bad that
my ancestor was an animal.
At school I asked the teacher a question.
“what
,
” I
asked,
“is an ancestor?”

“
Ancestors,
”

the
teacher
said,
“
are
the
fathers
and
mothers
of
your
grandmothers
and
grandfathers.
”

I knew then that I was different from everyone else in the world.
For
several
months
my
dreams
were
full
of
large
dead
animals.
I
looked
carefully
at
all
my
relatives, and stood a long time each day in front of the mirror.
One day, I was sure, something
was going to happen to my face.
“
Tell me about my ancestor,
” I
said to my mother.
“
Did he really have a tail and a horn on the end
of his nose?
”

She fetched the photograph down from the upstairs, and for the first time I saw a man with a gun,
standing behind the animal.

“
There
’
s a man!
” I
shouted.
My mother looked at me strangely.