第一节： 单项填空(共15小题， 每小题1分， 满分15分).
从A.B.C.D四个选项中选出可以填入空白处的最佳选项， 并在答题卡上将该项涂黑。
21. I often have conversations with John over _______telephone, while I keep in _____touch with Tom by ______letter.
A. /; the; the B. the; /; / C. /; a; / D. the; /; a
22. ____is mentioned above, the number of the cattle here has been limited to 200.
A. It B. Which. C. That. D. As
