What does the speaker believe about making a mistake?

• A. It is possible I made a mistake.
• B. It's impossible I made a mistake.
• C. I definitely didn't make a mistake.
• D. I didn't check the number.

Answer: (B)

The main concept is expressing certainty about whether a mistake occurred. Saying “It’s impossible I made a mistake” shows the speaker believes that making a mistake cannot be the case—there’s no chance they erred. That strong claim of impossibility best captures what the speaker believes about the possibility of having made a mistake.

The other ideas don’t fit as well because they express doubt or a different kind of certainty. Saying it’s possible I made a mistake leaves room for error and doesn’t communicate the same absolute belief. Saying I definitely didn’t make a mistake communicates a firm denial, but it doesn’t use the idea that the event is impossible—it’s a strong statement of not having erred, not a claim about impossibility. The last option about checking the number is irrelevant to what the speaker believes about making a mistake.