1. China has thousands of islands ,______ Tainwan Island is the second largest island .
A .of them B .among which C .one of which D .among them
2. _____ is known to everybody ,the earth travels round the sun once every year .
A . As B . It C .That D .What
3. The old man had two sons , _____are working in foreign country.
A .both of them B .both of whom C .and both of whom D .neither of them
