两种微粒的质子数和电子数都相等,它们不可能是: A、一种阳离子和一种阴离子 B、一种单质分子和一种化合物分子 C、两种不同的离子 D、一种原子和一种分子 答案:ALike distance runners on a measured course,all of us will move through time in a roughly
predictable pattern.
In the first stage of our lives,we develop and grow, reaching toward the top of
physical vitality(活力).
After we grow up,however, the
body begins a process of gradually wearing out.
A new awareness of physical fitness may help lengthen
our years of health and vitality,yet nothing
we do will work to stop the unavoidable force of aging.
Most of the changes of aging take place deep inside
the body.The lungs become less able to take in
oxygen.Powerful muscles gradually lose their
strength.The heart loses power and pumps less blood.Bones grow easier to break.
Finally, we meet a stress,a stress that is greater than our physical resistance.Often,it is only a minor
accident or chance infection(a disease caused by virus),but this time,it brings life to an end.
In 1932,a classic
experiment nearly doubled the lifetime of rats,simply
by cutting back the calories in their diet The reason for the effect was then
unknown.
Today, at the University of California at Berkley, Dr.Paul Seagle has also greatly lengthened the normal
lifetime of rats.The result was achieved through a special
protein limited diet,which had a great effect on the chemistry
of the brain.Seagle showed that within the brain,specific chemicals control many of the signals that
influence aging.By changing that chemical balance,the clock of aging can be reset.
For the first time, the mystery of why we age is being
seriously challenged.Scientists in many fields are now making
striking and far-reaching discoveries.
An average lifetime lasts 75 years,yet in each of us lies a potential for a longer life.If we could keep the vitality and resistance to
disease that we have at age twenty, we would live for 800 years.
1.What does the underlined word “it” refer to?
A.Physical
vitality. B.Stress. C.Aging. D.Physical
resistance.
2.Which of the following is not a change of aging?
A.People
gradually lose their muscle strength.
B.Bones tend to
break more easily.
C.The heart
loses power and pumps less blood.
D.The lungs
become unable to take in oxygen.zxxk
3.The author believes the following except that .
A.human's life
pattern is predictable
B.physical
fitness can't stop the force of aging
C.human's
lifetime will last longer than 75 years
D.all of the
changes of aging take place deep inside the body
4.How did Dr.Paul Seagle
lengthen the lifetime of rats in his experiment?
A.By keeping
their physical fitness. B.By cutting
the calories in their diet.
C.By resetting
their clock of aging. D.By limiting
the protein in their diet.
5.What is probably the best title for the article?
A.Two Great
Experiments
B.The Mystery
of Human Life
C.The
Breakthrough in the Study of Aging
D.Ways to
lengthen Human Life