moment l got home

moment l got home
The moment I got home,my wife asked me________I had been to the hospital.
A.when 　　B.why　　C.whether 　　D.that
【答案与解析】C　考查宾语从句的引导词.若选A项或B项,宾语从句的时态应为一般过去时;that用来陈述事实,而前面是动词asked,此处表示疑问,所以选whether.
不明白为什么选择B项,宾语从句为什么要用一般过去时?
还有如果选择A的话,宾语从句不应该是过去将来时吗?