【正确答案】 B

【答案解析】[考点] when的用法
[解析] when“这时(突然)”。常见的搭配有：be doing…when…；be about to do…when…；had done…when…。例如：I was walking in the street when someone called me from behind.我走在街上，突然有人从后边喊我。I was about to go out when he came in.我正要出门，突然他进来了。