单选题 He had scarcely left the railway station ______ it started to rain.
A. than B. then C. when D. since

【正确答案】 C
【答案解析】[解析] 句子的大意为：他刚离开火车站，天就开始下雨了。when在这里等于at that time。所以C项符合题意。