15. ---I don’t know how to write the article assigned by our professor on international trade.

　 --You should have ______ your attention on the lecture that ______ how international situation affects exports and imports across the globe.

　　 A. put; concentrate on　　 B. paid; talked about　　

C. fixed; dealt on　　　　 D. focused; focused on

14. The operation room in every hospital has to _______bacteria of any kind so that the patient being operated on doesn’t get infected.

　 A. keep free from B. make it free from C. to be made free with D. be kept free from

13. The father has been ____ for many years in order that his only son can be ____ with higher education.

A. fighting; served　 　B. struggling; equipped

C. working; offered 　D. laboring; received

12. People often make a mistake about my nationality.　 I was born of Chinese parents , _____, I look ______ but I was born and grew up in America, so I am an American.

A. however; Chinese　 B. therefore; Chinese　　

C. so; the Chinese　 D. therefore; a Chinese