2015—2016 外研版选修七 module4 grammar (3)
2015—2016 外研版选修七 module4 grammar (3)第3页

2. 若主语不同而谓语助动词,情态动词相同,则省略后面的助动词或情态动词。 Jack must have been playing football and Mary (must have been) doing her homework.