Don’t eat too much chocolate, or you can ______ weight quickly.

He ________ me to come to my birthday party, but until it was over he didn’t appear at all.

Have you ever wondered why some of the smartest students in your class sometimes ________ failing exams? 

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

Though he failed in the experiment again and again, he didn’t______, and at last, he made it.