Mr. Smith, who often helped passers-by repair their bikes, said that what he did was not paid but _______.
| A．relevant | B．optional | C．suitable | D．voluntary |
Hurry up!The train ______. You know it ______ at 8:30 am.
| A．leaves; leaves | B．is leaving; is leaving | C．leaves; is leaving | D．is leaving; leaves |
In recent days ,with the help of our teacher , I have made ___ great progress in _____mathematics.
| A．a; the | B．/ ;/ | C．/ ; the | D．a ; / |
Mrs. Green always helps her mother even though going to work _________most of her day.
| A．takes out | B．takes down | C．takes up | D．takes off |
We have to admit that the biggest___________ facing the ecosystem is limited resources and the worsening environment.
| A．mission | B．challenge | C．scale | D．contribution |
Your task will be to examine the___________ of constructing a new factory in the United Kingdom.
| A．motivation | B．appointment | C．adjustment | D．possibility |