Find and correct the mistake

[nhohatmit]

Plz help me. Show me why it is incorrect. Thanks so much.
1.The amounts of oxygen and nitrogen in the air almost always remain stable, but the amount of water
A B C
vapor vary considerably.
D
2.A dolphin locates underwater objects in its path by doing a series of clicking and whistling sounds.
A B C D

18. In the second half of the nineteenth century, textiles from the southwestern United state, particularly fabrics woven by the Navajo people, _____________________ .
(A) began to be used as rugs
(B) rugs began to be used
(C) as rugs began to be used
(D) began to used them as rugs
A B C D
33. Some nematodes are very tiny that it Is necessary to view them through a microscope.
A B C D
34. It is estimated that a scientific principle has a life expectancy of approximately a decade before it
A B C
drastically revised or replaced by newer information.
D
35. The more arid the continent, the less the amount of annual precipitation _______________ .
(A) runs off that
(B) runs it off
(C) that runs it off
(D) that runs off

[tubi]

1. D -> varies
2. A--> to ( object to)
18. A
33. B--->so tiny ( “ so—that” structure)
34. D --> is drastically
35. D ( I’m not sure ^0^)