Complete the sentences with FOR or SINCE.
1 I've been playing the piano ...... five years.
2 He's been working on that project .............two months now, and he still hasn't finished!
3 You've been working on the computer …………..six this morning. Have a break !
4 We've been going to Latin American dance classes ………..2004, and we're quite good at the tango now.
S I've been reading this book ……… three weeks now.
6 We've been waiting here ……... hours !