He studies the subject _____

If a healthy environment is gone, ________ everything that our life depends on.

ld you please have my car ready today— Sure. The damage is not that serious, so it ______ be ready by 5:00 p.m.

rry __________ for my illness, I wouldhave come to give you a hand

I find it difficult to learn English better!—_________you don’t give up(放弃)，your dreams will come true.