Some biologists believe this is an ancient survival strategy, _______ a diet with 30 percent fewer calories than usual increased life span.
—What do you think of the play?—Terrible! I’ve never seen _________ one.
Between 4.5 and 3.8 billion years ago, the earth became so ______ that it was not clear whether the shape would last or not.
_______ Japan’s nuclear crisis (核危机) will be solved in 2011 is not known yet.
Little Tommy was not willing to tell the teacher _______ he had done before.
The boy lying in the bed _______ to his friend that a cock _______ an egg yesterday.