问题补充：
Trains with the first letter D or Z can run a speed of more than 200 kilometers an hour when it travels the desert.
A. with; cross
B. in; through
C. at; across
D. for; in
答案：
A. with; cross
B. in; through
(答案→)C. at; across
D. for; in
解析：考查介词：句意：首字母是D或Z的火车在沙漠行驶的时候，可以达到每小时200公里的速度。At a speed of以…速度，travel across穿过…的表面，选C。
