Grammer Exercise 2 (改错题) B. Each of the following sentences contains ONE mistake. Find it out and correct it. 1. Henry mustn' t be at home because he phoned me from the farm just now. 2. Jack is a bilingual person. He may speak English and Japanese. 3. Mary can know the answer to the question. I ' m not sure. 4. You mayn' t tell anyone about this — it' s a secret. 5. Mother is out, so I must look after the shop.