The question refers to an "above reaction sequence", but the actual reaction scheme/image is not present in the prompt. Also, the options $A, B, C, D$ are listed without any structures or descriptions.

Because of this, the product $B$ cannot be determined from the given text alone.

What is missing?

To solve this organic chemistry question, I would need at least one of the following:

1. The reaction sequence showing the starting compound and reagents, or
2. The structures corresponding to options $A, B, C, D$.

Without the reaction sequence, any choice among $A, B, C, D$ would be a guess, not a valid chemical derivation.

Comparison with stored answer

The stored correct answer is given as A, but since the essential reaction information is missing, I cannot independently verify that result.

So, I do not agree with the stored answer on the basis of the provided data — not because $A$ is necessarily wrong, but because the problem statement is incomplete and unsolvable as given.