31．—What’s the matter with Christine—A letter from her parents inCalifornia________an attack of homesickness.

Do you need any help, lucy –Yes. The jobis _____I could do myself.

Black holes can not be seen directly, so determining the number of them is a___________ task. [ ]

ng the reconstruction of the city, many modern tall buildings went up ______ old shabby houses were torn down.

_____ will you be in Guangzhou—I am going to leave for Beijing in twomonths’ time.