The theme of The King’s Magic Drum, is to always be honest. You can be rewarded by telling the truth instead of lying.
The answer to the question is b
they don't want the workers to hear them
Mrs. Price is Rachel's teacher. We don't get much description of her, but if I had to make one up, I'd probably guess she has long hair in a tight bun, a long pleated skirt, and a broad crocodile snout with smoking nostrils. Typical Teacher from the Black Lagoon.
Okay, I don't want to be too unfair with Mrs. Price; maybe she's just having a really, really bad day too, but even so, she's pretty disregarding of Rachel and her feelings.