31.  The professor started his lecture.

32.  He cleared his throat and stopped talking for a while.

33.  The professor turned his back and quickly wrote a series of equations and complex symbols on the blackboard.

34.  " he ended his word in a light tune with a cold smile.

35.  You can see when the professor starts his class.

36.  From the professor's facial expression, I could see his appreciation on her.

37.  Some of my classmates were quite in agreement with his words.

38.  I couldn't believe the boy was a sophomore because in accordance with my observation, his face was bright and full of curiosity which was so "convincing" that I didn't think it was necessary to ask his grade.

39.  Unlike many other boys' bronze-colored complexion because of playing basketball under the sunshine for a long time , his is quite fair.

40.  He stood there silently , lowered his head, and got headphones in his ears and an i-phone in his hand.