1.I ______(save) $50 a month and I srared in January.So by the end of the year I ______(save)$600.
我的答案:saved正确答案:save,have saved不知为什么?请翻译中文
2.We`d better wait till 15 December.David_____(have)his exam by then,so he will be able to enjoy himself.
我的答案:has 正确答案:will have had不知为什么?请翻译中文