Question

The missing boy was last seen ___ near the river.

　A. playing　 B. to be playing　　C. play　　D. to play
选哪个？
感官动词在被动语态中则to 不能省掉的吧

Answer 1

A

感官动词 + doing/to do
感官动词see, watch, observe, notice, look at,hear, listen to, smell, taste, feel + do表示动作的完整性，+doing表示动作的进行性。例如：
I saw him work in the garden yesterday.
昨天我看见他在花园里干活了。（强调\"我看见了\"这个事实）
I saw him working in the garden yesterday.
（强调\"我见他正干活\"这个动作）昨天我见他正在花园里干活。

典型例题 1）They knew her very well.They had seen her ___ up from childhood.　
A. grow　B. grew　C. was growing　D. to grow
答案：A。因题意为，他们看着她长大，因此强调的是成长的过程，而非正在长的动作，因此用see sb do sth 的句型。

2）The missing boy was last seen ___ near the river.　
A. playing　B. to be playing　C. play　D. to play
答案A. 本题强调其动作，正在河边玩，应此用see sb. doing sth句型。

Answer 2

答案为：A see为感官动词 感官动词+doing
see sb.doing sth.看到某人正在做某事。本句为被动语态。句意为：那几个不见了的男孩最后一次被看到的时候正在河边玩耍。被看到的时候还是正在玩耍，进行时。

Answer 3

如果是我，就选第一个答案A, 第二个答案是可以接受的答案但不是最佳答案。第三个和第四个答案根本不可能，既缺乏义理理据也没有语法理据