22．Lawrence Craven, a doctor from the USA，is the author of several published reports, one of______ introduced the idea in 1953 ______aspirin could reduce the risk of heart attacks．

．China is playing an important role in the world. That’s_______Laura has come to study Chinese.

It’s the first time ______ he has helped us. 

Children of this age should be reminded of________ to do in public places.

— Did you remember to give Jenny the money? — Yes. ________ I saw her, I’m sure.