—I can never forget the day ___ we spent together in the summer camp．

—Well, especially the day _______it suddenly began to rain in the middle of the night．

A．when; when

B．which; when

C．what; that

D．on which; when

建筑工程质量事故常有发生，因此，必须采取有效的措施，对常见的质量问题和事故事先加以预防，并对已经出现的质量事故及时进行分析和处理。( )