Question

1. The missing boy was last seen ____ near the river. A. playing B. to be playing C. play D. to pl

1. The missing boy was last seen __A__ near the river.
A. playing B. to be playing C. play D. to play

不是“被看见”吗？为什么不选B？

8. You can’t have the horse ___C__ all the way. It’s too hot.
A. run B. to run C. running D. to be running

让马去跑 意思是让某人做某事 不是用have sb do么 为什么不选A

Answer 1

1. 考点: see sb. doing sth. 看见某人正在做某事
变成被动语态后, 就成了: sb. be seen doing sth.
不能用sb. be seen to be doing 哟！
因此此题选A不选B。

8. 注意这两者的区别:
have sb. do sth. 让某人做某事.(某人做了某事, 强调动作已结束)
have sb. doing sth. 让某人一直做某事. (强调动作的延续性, 动作还未结束)
此句的意思是: 不要让马一直跑, 天气太热了.
由句意可知, 这儿是强调动作的延续性,因此应选C而不是A.

Answer 2

针对这道题 The missing boy was last seen __A__ near the river.
A. playing B. to be playing C. play D. to play

解析：see 感官动词可以加do sth/doing sth，do这个不定式前面其实省略了to，这个道理等同于使役动词have sb do sth中也被省略的to一样。在被动语态中必须要补充to，即 be seen to do sth。

注意：see sb doing sth本身并没有省略to，所以在被动语态中不需要补充to，即 be seen doing sth。所以不选B

第二题其他网友解释了，have sb doing sth 让某人一直做某事

Answer 3

此处强调最后一次看到时，男孩正在玩，而非已经或曾经玩过。所以用doing,而to do结构在sb be seen to do sth 中表shi
表示动作曾经发生过。