四、下面每句都有一个标点符号错误，该用标点处未用标点或标点符号用错，改正错误或补写标点。

　　1. I doubt that he can answer your question

　　2. In short employees must work hard and creatively.

　　3. We are considering Boise, Idaho or Phoenix Arizona as a possible site for our factory.

　　4. Everybody knows that, we have a very challenging sales quota to fulfill this year.

　　5. The aircraft exhibition will be open seven days a week from 9 am to 6 p.m.

　　6. The machines arrived today, we plan to install them next week. 7. If you desire additional information please sign and return the enclosed card.

　　8. Although, he joined the firm only last year, he is already senior to me.

　　9. The rent is reasonable, moreover, the location is perfect.

　　10. They have been working for hours without a moments rest.

　　答：1. dispensable →indispensable 2.Comparing →Compared

　　3. is become →is becoming/has become 4. fluent →fluently

　　5.do →doing 6.them →they 7.a →an

　　8.which →whose或which stipulations of which 9.by →with

　　10.the TV networks were commended by the editor →the editor commended in the TV networks