1. John is in his room, he (has been sitting) there since the morning.
2. For two hours now we (have been talking) about it and we haven`t come to any conclusion yet.
3. By May my grandfather (has been working) at the factory for 20 years.
4. I (have been trying) to get him on the phone all day.
5. I (have been writing) the letter for an hour when mother called me.
6. He (has been working) on his book for a year soon.