1 stop作prevent解的时候，句型为stop sb (from) doing sth. 这里from可有可无。有from则其后的doing无疑为动名词，from介词短语作状语。问题是如果没有from, doing究竟是动名词还是现在分词，并没有统一的观点。可能有人认为doing为现在分词作宾补，有人认为stop后接动名词复合结构作单宾语。公说公有理，婆说婆有理。COCA语料库有如下例句，当doing前为属格代词时，stop无疑后接动名词复合结构作宾语。当doing 前为宾格代词时，还是说不清楚，因为在非正式语体，动名词的逻辑主语可以是宾格。

And I wasn't able to stop his hurting other people. I wasn't able to stop his hurting himself.

He knows that nobody is perfect but that doesn't stop him trying to do his best.

Hillerman did not let criticism stop him from writing about a people he admired and studied.

所以，争论这个意义不大，并不影响对句义的理解。这也是为什么现代语法对doing是现在分词还是动名词不作区分的原因之一。类似情况还有have difficulty （in) doing sth. 当介词in省略后，doing是动名词还是现在分词也是有争论的。

2 I’m sorry to see you being so sad about it

see作为感官动词，是不可以后接静态动词的现在分词作宾补的。所以这个句子为错误。但see可以后接形容词作宾补，此时严格讲see并不是感官动作，而是认知动词。所以，这个句子应删去being, 直接用形容词作宾补。下面为类似的词典例句：

I hate to see you unhappy. （牛津）