We must______ using plastic bags in order to protect our earth..
I don’t know if it _______ tomorrow. If it _____, we will go out for a picnic.
An old man was found ______ in his house. Luckily, he was taken to hospital in time.
The old scientist devoted most of his time __________ the space science.
—Excuse me, Mum. When can we have dinner?—Not until it in half an hour.
— Do you know whose magazine is it?— I think it be Lily’s, for we can find her name on the cover.