—Is it necessary to look up every new word when I come across it in reading?—No. You ________， because you are likely to guess the meaning from the context.

. --- I'm sorry. I ____________ the bike to you yesterday. But I was too busy at that time. --- Never mind.

He _____ be really difficult at times even though he ,generally speaking, is a nice person. 

 —Who’s that boy reading in the study ? Is it David?—It __________ be David. I saw him go home just now.

 Everyone ______ be polite to the old people.