Prompt 1-A is neither learning English nor reading novels;
Hint 1
The second technique has assumptions, so skip it first.
The third hint-some people say that B is doing math problems or learning English, but it is not the case:
The third hint
The fourth tip-C is neither reading novels nor reading English:
The fourth hint
Because four people have to do one of four things, and they are different from each other, Ding is learning English.
It is observed that A and C are not reading English or novels, one is doing a math problem and the other is writing a letter.
Then look at the second hint, "If A is not doing math problems, then D is not in your English".
Because it has been confirmed that Ding is learning English, A is doing math problems.
So C was writing a letter and further learned that B was reading a novel:
Inference result