major primary structure

例句：

1. 1. The major of the university is in engineering.
   大学的主修是工程学。
2. 2. The main reason for their success is their hard work.
   他们成功的主要原因在于他们的努力工作。
3. 3. The main function of this machine is to cut wood.
   这台机器的主要功能是切割木材。