I have been watching（or:have watched) TV for two hours.
是的,用介词for,表示持续一段时间,要用完成时态
for在做连词,表示目的等时来不引导一段时间,如下：
for
KK:[]
DJ:[]
prep.
1.为,为了
They fought for national independence.
他们为民族独立而战.
This letter is for you.
这是你的信.
2.代替;代表
We used boxes for chairs.
我们用箱子当椅子坐.
3.因为,由于
I am sorry for what I said to you.
我后悔不该对你讲那些话.
4.在(指定时间)
The meeting is arranged for 9 o'clock.
会议安排在九点钟.
5.(表示时间、距离等)达,计
You can see for miles from the roof.
你站在屋顶上可以看到数英里之外.
6.对于,关于;在...方面
I am too old for the job.
我年纪太大,做不了这工作.
7.为得到,为赢得
He sent the waiter for a packet of cigarettes.
他让侍者去拿一盒香烟.
8.以...为代价;以...交换
He sold his car for 500 dollars.
他以五百元把车卖了.
9.当作,作为
Do you take me for a millionaire?
你是不是把我当百万富翁?
10.赞成;支持;倾向于
Are you for the government or against it?
你是支持还是反对政府?
11.朝...方向去;往,向
He left for Taipei.
他出发去台北.
12.就...而言
She is sophisticated for her age.
就年龄而言她是世故了一点.
conj.
1.因为,由于
We must start early,for it will take two hours to drive to the airport.
我们得早点动身,因为开车去机场得花两个小时.
