After many ______(实验), he finally succeeded in finding the solution to the difficult problem.
He is very d__________ because he failed in the examination.
Hearing what he was saying, a question naturally p__________ itself in my mind.
I feel it a great __________ (荣幸) to give a lecture to you.
The c__________ of stamps is housed in a fine building.
This medicine will give you some r__________.