You _____ be tired; you have been working for so long a time,but he _____ be tired; he has just begun to work.
---- My baby has a heart trouble. ---- Did the doctor find it difficult ______ ?
---- Where did he go? ---- He went to another store ______.
---- Why was the official meeting called? ---- ______ new officers.
Because of air pollution being greatly reduced, this city is still ______.
---- I didn't hear you come in last night. ---- That's good. We tried_____ noisy.