Only when __________________ permission _______________ allowed to enter the lab.

Carbon dioxide ___ from burning fuels is the most common of the so-called greenhouse gases.

——Your coffee smells great！——It’s from Mexico. Would you like ____  ?

— What do you think of Zhang LiangYing's English songs? — Very attractive and lively. Almost no other Super Girls can sing _____ at present, I think. 

Scientists photographed for the first time ever _____ wild gorillas used a stick to test the depth of a pool before getting into it, according to a recent study.