根据语境可加宾语或宾语从句，状语或什么也不加
如:
I am doing homework.
The students are reading in the classroom.
如：
1.He wrote me a letter，telling me that he would come here.（that从句做现在分词 telling 的直接宾语 ）
2.Not realizing that he was in great danger，Eric walked deeper into the forest.（that 从句做现在分词 realizing 的宾语）
3.Knowing that his mother would come to see him ，the boy jumped up with joy. （that 从句做现在分词 knowing 的宾语）
现在分词用法:
（1）现在分词作表语（含有“使 ...... 怎么样，令 ...... 怎么样”的意思，所以有“主动”含义）
The story was very amusing.这个故事真逗。
That book was interesting.那本书很有趣。
常见的还有：
exciting 令人激动的
interesting 使人产生兴趣的
disappointing 使人失望的
tiring 令人疲惫的
moving 让人感动的
（2）现在分词作定语（相当于一个形容词）
It was an exciting finish.结局让人激动不已。
He is a charming person.他是个魅力四射的人。
现在分词还可以作后置定语（修饰谁，就和谁是主动关系）
The girl standing behind the counter served me.站在柜台后面的那个女孩接待得我。
The car waiting outside the garden is mine.等在花园外面的汽车是我的。
（3）现在分词作状语（表示一个伴随发生的动作）
Following my dog, we ran into the garden.跟在我的狗狗后面，我们跑进来花园。
She sat in bed reading.她坐在床上读书。
