One day as a teacher walked into the classroom, he heard a low voice: "Here is the teacher, I’m sure the unfair fellow (不公正的家伙) is going to talk about putting in commas. "It was Bill’s voice. He was talking with the boy next to him. The teacher didn’t get angry. He said nothing about it but he began, to talk about putting in commas, and then he wrote on the blackboard the sentence: "Bill says the teacher is an unfair fellow." The class laughed and Bill’s face turned red. "Now," said the teacher, "I’ll show you how important commas are." He put two commas in the sentence, and read, "Bill, says the teacher, is an unfair fellow."

Bill’s face turned red because he knew ______ heard what he said.

A． his classmates
B． the boy next to him
C． the teacher