homework是不可數名詞. 
老師上課説do some homework,意思就是做一些家庭作業,homework沒有用複數形式。此外,它的根詞是work,工作,本身也是不可數名詞。
是不可數名詞。
n. 家庭作業,課外作業Have you finished your homework today?
你今天完成作業了嗎
I have a mountain of homework to do.
我有一大堆準備工作要做。
More and more people prefer to do homework.
越來越多的人更願意做在家中進行的工作。
You can't watch TV until you've done your homework.
做完家庭作業之後你才能看電視。
I can't come out to play until I've finished my homework and my chores.
我沒完成作業和家務之前不能出去玩。