What he told me to do was ______ I should get fully prepared before the interview.A. whatB. ifC. whichD. that

此题考查的是宾语从句的用法。在句子"What he told me to do was ______ I should get fully prepared before the interview."中，"What he told me to do"是主句，而"______ I should get fully prepared before the interview"是宾语从句。宾语从句中，当从句不缺少成分时，应使用that引导，且that在从句中不充当任何成分，也不改变从句的含义。因此，正确答案是D选项。