D that,that,首先The reason____he gave 是定语从句，reason在从句中做宾语，所以用that而不用why。。而后句是表语从句，引导词只能用that。句型为the reason is that。。。A what;which。 what it was，what做was的宾语，后句是which引导的非限定性定语从句
D B
D A 对的
