______ the bus until it ______..

Another drug that has helped improve people’s health is penicillin, _________ is _________ by many _________ one of the most important medicines.

Why _____ go to the zoo with us? [ ]

You’d better not always look up the new words __________ the dictionary while reading. Sometimes we need to guess. [ ]

As we know, in our Chinese history _____ was a time when industry was only a home business.