the reason why he failed in the examination is [ ]he had not worked hardA because B that C for D because of 这题中为什么选B 呢
问题描述：
the reason why he failed in the examination is [ ]he had not worked hard
A because B that C for D because of 这题中为什么选B 呢
答
括号前面的部分主干是“The reason is",它并不是一个完整的主谓宾句子,而且“why”是引导定语从句的关系副词.括号后面是一个完整的主谓宾句子,因此,括号上需要填一个宾语从句的引导词将后面的句子作为一个整体宾语,这样,整个句子就成为一个完整的句子了.只有that才符合要求