Do you know ________ in Japan?
A.when nuclear(核)accidents happened
B.when did nuclear accidents happen
C.when nuclear accidents happen
D.when do nuclear accidents happen
网友回答
A解析考查点：宾语从句．解题思路：宾语从句的语序用陈述句语序，故排除B、D选项，主句是一般现在时态，从句的时态根据情况而定，故从句用一般过去时态．故选A．