After he _______ in a factory he opened a small business.
A. has worked
B. had worked
C. would work
D. was working
Đáp án B
I think we should have our house painting because it looks too dirty.
The situation is serious. Something must ___________ before it’s too late.
Species that have already lost habitat because of deforestation were given higher priority in the plan because of their greater risk of extinction.