下列各句中，没有语病的一句是（ ）

ering your salary, you should ________ at least 100 dollars a week.

He __________ everywhere for materials and finally his efforts paid off. The medicine __________ to be very effective.

I can think of many cases students obviously know a lot of English words and expressions but couldn’t write a good essay．

How much are the two pairs of shoes? —They are not expensive. I think fiftydollars ______ enough.