I’m amazed to hear that Frank and Linda have broken up.—________. They were walking happily hand in hand last time I saw them.

____ several times, the young scientist still kept ondoing his experiments.

He____know the answer, but I’m not sure.

We all felt ______ after watching this ______ match.

Can you tell me the difference between the words “require” and “request” ? I sometimes get puzzled by their meanings.