--Whomdidyou___thepacketatthepostoffice?--Jack.There____massesofworkforhimtodo,buthemanagedtofinishtheworkasrequired.A.havefetched,wasB.havefetch,wereC.havefetched,wereD.havefetch,was第一个空我明白运用的是

　　--Whomdidyou___thepacketatthepostoffice?

　　--Jack.There____massesofworkforhimtodo,buthemanagedtofinishtheworkasrequired.

　　A.havefetched,wasB.havefetch,wereC.havefetched,wereD.havefetch,was

　　第一个空我明白运用的是havesb,dosth,那第二个是根据什么选择的,massesof修饰名词作主语时谓语动词怎么选择单复数