Many teens don't get enough sleep because they have too much homework to do, which ________ them up at night.

.I would appreciate_____ very much if you could give me some advice on TOEFL.

____ students are practicing ___ English with each other at the English corner. 

(2011·江苏高考)—I left my handbag on the train, but luckily someone gave it to a railway official.—How unbelievable to get it back! I mean, someone ________it.

 To their great fear, they found _______ in the heaviest snowfall they had ever had.