When the space ship was ____, I could really feel the high gravity. 

In the time of HINI, scientists ____ their spare time to conduct research on the ways of curing the disease.

Many students signed up for the _______ race in the sports meeting to be held next week.

I don’t              when I fail_______ something.

I wonder how it ____ that Chinese climbers successfully finished the torch relay on the Mount Qomolangma, where the air is so thin.