The reason ________ she missed school this morning was ________ she had to look after her sick grandpa．
A.why; thatB.because; whyC.that; becauseD.which; that在线课程A
这是个复合句。reason后面是个定语从句，was后面是个表语从句。reason作先行词时，关系副词用why；reason作主语时，其后面的表语从句只能用that引导，故答案为A项。