In this case, you must reply. Say thank you to the teacher or something. You can also ask him what you want to ask, what you don't understand and what you don't understand. When your tutor is not busy, he will definitely reply to you, but if you know how to send a thank you or something, he won't reply to you. Just wait for the meeting. You must reply. This is a basic question of politeness. Don't worry too much about others, such as being afraid of adding burden to teachers. It's not necessary. The teacher will not have too much burden to read your email, just like replying to a person's QQ message. Therefore, it is recommended to reply.