Listen! Is Mary singing in the next room—No. It _______ be Mary．She has gone to Shanghai for an important meeting.

______ the maths problem is difficult， I’ll try very hard to work it out.

When Peter __________ the car door, he found the key left in his carSo he had to call for help

1Private cars are becomingvery popular though most of them still ______too much

When will you leave for Paris for a visit? —–_______next month