Correct Option (B)
The passage explicitly states, "Her bored classmates suddenly stopped their noisy chat..." This phrase directly indicates that the classmates were experiencing boredom, which led to their chatting. The cessation of their noisy chat upon Cynthia's excellent performance further confirms their initial disinterest in the ongoing auditions.
Incorrect Options:
- Option (A): The passage provides no information to suggest that the classmates were chatting because it was their turn to perform next. This is an unsupported inference.
- Option (C): The classmates' chatting occurred prior to Cynthia's performance, as indicated by their sudden silence once she began to perform well. Therefore, their chatting could not have been a reaction to Cynthia's acting, which had not yet taken place.
- Option (D): The passage does not offer any details regarding the teacher's control over the students. This option introduces an external factor not supported or addressed by the given text.