Which of the following situations provides the BEST example of a trainer demonstrating content expertise?

Which of the following situations provides the BEST example of a trainer demonstrating content expertise?

A.
A trainee brings an instructional error to the trainer’s attention and the trainer apologizes and thanks the trainee.

B.
A trainee asks a question about the course material and the question is completely and accurately answered by the trainer.

C.
Whenever a trainee requests a copy of a homework problem, the trainer always provides it the next day.

D.
Whenever a trainee suggests a more meaningful method of presentation, the trainer graciously accepts and implements the idea.