1) They are busy now, they are discussing) an important problem.
2) They have been discussing it since two o’clock.
3) Both grown-ups and children are fond of playing computer games.
4) My friend has a good ear for music.
5) He has played the piano since five years old.
6) Look! The boys have broken the window and now they are running away.
7) Let’s go, the train has already arrived.
8) When did you visit our city for the first time?
9) He had collected thousands of stamps with pictures of famous people before he gave up philately.
10) You shouldn’t speak loudly when you are fishing/