16. They took _______ measures to prevent poisonous gases from escaping.

A. fruitful

B. beneficial

C. valid

D. effective

17. With the help of a metal detector, they discovered that wreckage lay _______ over a 2,000-square-feet area, often buried beneath sand and seaweed.

A. scattered

B. separated

C. dispersed

D. distributed

18. It was his wife’s encouragement that had _______ his through the bad times.

A. delivered

B. relieved

C. sent

D. brought

19. The distance from the Earth to the spacecraft is often determined very accurately

from the time _______ between two radio signals.

A. interaction

B. alternative

C. interference

D. interval

20. Finding himself trapped in the Death Valley, he had a sudden feeling of _______.

A. despair

B. desperate

C. frightened

D. dreadful
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