A) She believed her mother's thoughts were unimportant because she expressed them imperfectly.
Bias is when you have unfair feelings for or against a person or thing because of prejudice. In Option A, Amy Tan demonstrates language bias because she is unfairly judging her mother's thoughts. She doesn't believe her mother's thoughts to be important since her mother had trouble expressing them perfectly. Option C and D do not show any unfair feelings for or against her mother.