People _________ rivers for transportation since the beginning of history.
A. used B. have usedC. use D. had used
The new headmaster looks _________ to all the teachers and students of the school.
A. friendly B. seriously C. probably D. gently
If the kids stay indoors all the time and get no exercise, they _________ weak.
A. become B. have become C. will become D. became
At the meeting the boss was explaining his plan while his secretary_________ the notes.
A. is taking B. was taking C. has taken D. takes
Mr. White spent about one hour and a half _________ the accident report yesterday evening.
A. write B. written C. writing D. to write
To live a green life, we try_________ more energy and produce less pollution.
A. to save B. save C. saves D. saved
