Scientific researches show that to __________ a language one had better often get exposed to it.

Only after one has become a parent _____ how great his parents are．

The English in the future will be quite different from the English of today. It is possible that some English words may even ________ completely.

Mr. Wang _______drive to work, but now he _______there by bike to keep healthy.

_____ are these red trousers— 10 dollars.