The word "those" in paragraph 1 refers to:
A.nitrates
B.properties
C.particles
D.models

In the scientists' research, where did the pollutants come from originally?
A.arid areas
B.the Saudi Coast
C.Cairo
D.the Sahara desert

What is the purpose of the passage?
A.to convince the reader that calcium nitrate is bad
B.to inform the reader of a new problem in climate modeling
C.to show how calcium nitrate was created
D.to show where calcium nitrate was first discovered

What is the main idea of the first paragraph?
A.Signs of aging are easier to detect in animals than in plants.
B.Aging occurs in every living thing after it has reached maturity.
C.Not all signs of aging are visible.
D.The outward signs of aging may be seen in old people.

All of the followings may be the outward signs of aging EXCEPT ___________ .
A.the graying of the hair
B.the wrinkling of the skin
C.the decline in hearing and eyesight
D.the loss of appetite

What happens to memorization when the brain begins to age?
A.It works less.
B.It becomes forgetful.
C.It declines.
D.It slows down.

The word "brittle" as used in the second paragraph means ___________ .
A.soft and easily bent
B.hard and endurable
C.hard but easily broken
D.rigid and inflexible

According to the passage, what condition is responsible for many of the diseases of the old?
A.the arteries have become thickened and constricted.
B.the blood vessels lead from the heart.
C.the brain gets smaller in size.
D.bones become lighter and brittle

According to the passage, which of the following is NOT true?
A.All living things grow old.
B.Aging is unavoidable in any living things.
C.Plants show less signs of aging than any other living things.
D.Most body parts wear out during the course of a lifetime.

I'd prefer you not to drink tea at night.
A.Tea is not good for your health, especially at night.
B.You can drink tea whenever you like but not at night.
C.I'd sooner you hadn't drunk tea last night.
D.I'd rather you didn't drink tea at night.