=> III/ 1. to play -> playing 2. used to singing -> used to sing 3. for -> by 4. to not -> not to IV/ 1. It's very important to keep the environment clean. 2. I haven't spoken to her for three years. 3. She told me not to forget to send my parents his regads. 4. Trung was given a microcomputer by his parents on his birthday.
