题目

完形填空，阅读下列短文, 从每小题所给的A、B、C、D 四个选项中选出最佳选项。                                      Mr. and Mrs. Green were very worried about their son, Leo. He seemed to be dumb (哑的)   1 he was normal in every other way. Mr. and Mrs. Green tried everything to get him to 2 , but with no success.    When Leo was six years old, the best doctors in the town 3 him carefully, but could find nothing wrong. And he seemed to be smart. It was just that he 4 spoke.    There might be something wrong with his 5 ,  We __________ here at lunch time; we were delayed at the airport, though.A. could be      B. should be            C. must have been    D. would have been