动名词可以作补足语，例如，I saw him playing basketball on the playground at this time yesterday. 意思是昨天这个时候我看见他正在操场打篮球。
动名词除了做补足语还可以做主语，宾语，表语，定语和状语等等例如，Swimming is one of his hobbies.
这个问题由我来回答。动名词作主语的句子很多，通常有以下这几个动词来引导。
有see hear watch notice等等。下面我来举几个例子说明。
1：当我经过操场的时候，我看到他正在打篮球。
I saw him playing basketball when I passed the playground.
2:我正在公园里观看猴子们上下跳跃。
I'm watching monkeys jumping up and down in the park.
3:当我走进教室的时候，我听到他正在唱歌。
When I came into the classroom ，I heard him singing.
