Why does the passage begin with a description of the properties of calcium nitrate?
A.To give background information so the reader can understand the topic better.
B.Because calcium nitrate is the main idea.
C.They show how elements combine to create calcium nitrate.
D.To prove the existence of calcium nitrate.

Choose the best answer for the following sentences:
Mary worked hard _______ passing the examination.
A.as so to
B.with the aim of
C.so that to
D.in order not to

Choose the best answer for the following sentences:
He turned out the light ________ waste electricity.
A.not
B.for not
C.so that not
D.in order not to

Choose the best answer for the following sentences:
The boy tiptoed into the room _______ wake everybody up.
A.so as to
B.in order that
C.so as not to
D.not to

Which of the following may be a result of these particles?
A.The change of an ice age is increased.
B.We mav see more rainbows.
C.The greenhouse effects are increased.
D.We may see an increase in carbon dioxide.

Do the particles react with nitric acid?
A.No, but they continue to absorb the sun’s energy.
B.No, and the particles do not change.
C.Yes, but the changes are temporary.
D.Yes, and the changes are permanent.

What is the main idea of the passage?
A.There is a new particle called calcium nitrate.
B.Factories are polluting the environment.
C.Climate models have to be updated because of the new particle calcium nitrate.
D.Calcium nitrate lias chemical properties different from other dust particles.

__________(9)
A.for
B.at
C.with
D.against

_________(7)
A.take
B.get
C.have
D.make

Choose the best answer to the following questions.
After Mariana _______ her exam, I _______ her out to eat.
A.was finishing / would take
B.finished / had taken
C.will finish / have taken
D.has finished / will take