The young men walked _____ the forest and came to a big river at last. [ ]

I was about to get on the bus _________someone called.

Don’t litter the ground, boy. Look at the sign, “Rubbish must be thrown into the dustbin.”—Sorry, I’ll __________ right now.

Can you understand what I mean? — Sorry, I can ______ follow you.

Look, your sister is playing the piano over there.－She ______ be my sister. She has gone to America.