. _______ his return from Japan, Prof. Li went directly to his l

. _______ his return from Japan, Prof. Li went directly to his laboratory and started working with his colleagues.
A、Upon
B、At
C、Within
D、Over
【正确答案】：A
【题目解析】：A【句意】一从日本回来，李教授直接去了实验室，开始和同事们一起工作。【解析】“upon (on) + 表示行为的名词”相当于as soon as引导的时间状语从句。