These three college students are real heroes because they risked ______their own lives in order to save the drowning boy
问题描述：
These three college students are real heroes because they risked ______their own lives in order to save the drowning boys in the water.
A.having lost B:to lose C.losing D.of losing
是risk doing形式,为啥选a不行,不是过去发生的事吗
答
因为如果使用完成时态,不能用risk having done,而应该用 have risked doing这样的形式.