They arrived Beijing on the evening of May 24.A. at B. in C. on

问题补充：

They arrived Beijing on the evening of May 24.

A. at B. in C. on

答案：

解析：at在一点；in在一个空间范围；on在一个平面。句意：他们在五月二十四日晚上到达北京。结合语境可知他们应是到达北京某个范围内，故选B。