【Itwas,ishouldsay,verykindofyoutocomeallthewaytohelpthem,butyou___a.didn'thavetob.wouldn'thavedonec.mustn'thavedoned.mightn'thavedonei'dratheryoudidsomehouseworkwhenyouarefree,butyou_____.a.didn'tb.shouldn'tc.weren't】

　　Itwas,ishouldsay,verykindofyoutocomeallthewaytohelpthem,butyou___

　　a.didn'thaveto

　　b.wouldn'thavedone

　　c.mustn'thavedone

　　d.mightn'thavedone

　　i'dratheryoudidsomehouseworkwhenyouarefree,butyou_____.

　　a.didn't

　　b.shouldn't

　　c.weren't

　　d.don't

　　为什么选D不选A?