—Does John serve in the army?—No, but he________in the army for 8 years.
By hiking, people can __________ nature and enjoy a new kind of life.
-How did you find the rock music concert last night? -__________.
There were only __________ as ten years ago on the hill.
It is suggested that a study plan __________ right now.
I know one of the things I was unsure about was __________ hard it would be to climb this mountain.