for是介词,介词后面要跟“名词/代词”作为其宾语,或者跟相当于名词/代词的结构,比如动名词、宾语从句等。如果后面是动词,不能直接跟在介词之后,而要变成+ing形式,这种doing称为“动名词”。动名词具有了名词的特性,就可以放在介词后作为其宾语了。
I'm interested in watching basketball,not in playing it.
I need to know something about raising cats.
I'm interested in watching basketball,not in playing it.
I need to know something about raising cats.