用括号内所给动词的正确形式填空（共5小题；每小题1分。满分5分）
—I hear that Sam has gone to Beijing for his holiday.
—Oh, how nice! Do you know when he ________ (leave)? 
—What’s wrong with my computer, Jim?
—Let me see. Oh, it _________ (break) down. You’d better ask Mr. Li to mend it.
The reporter said that the UFO _________ (travel) from east to west when he saw it.
Look! The teenagers are making cards ________ (show) love for their mothers.
－That important problem __________ (discuss) for nearly two weeks.
－Yes, it’s hard for us to solve it.