重点句型有：

1. What do you like to do in your free time?2. How often do you go to the library?3. Can you help me with my homework?4. Why are you late for class?5. Where did you go on your last vacation?这些句型是三年级下册英语书中比较重要的，掌握了这些句型可以帮助学生更好地理解课文内容，提高英语口语表达能力。