下列各句中，没有语病的一句是

It is believed that a new kind of drug ______ by the scientists and they are hopeful that they will succeed in a few months

— You may make more mistakes if your paper is left_______ — Thanks a lot And would you give me some advice on how to polish it?[ ]

When you copy this paper, be careful not to ______ a single word.

I don’t like to travel to big cities becauseit seems to me that one city is very much like___ ．