The question refers to an "above reaction", but in the provided prompt the actual reaction scheme is missing. Also, the options $A$, $B$, $C$, and $D$ are blank.

So, the key chemical information required to determine product $B$ is not available.

Step 1: What is missing?

To solve this organic chemistry question, I need:

1. The reaction scheme (starting compound, reagents, conditions).
2. The structures of options $A$, $B$, $C$, and $D$.

Without these, product $B$ cannot be derived.

Step 2: Can the stored answer be verified?

The stored correct answer is given as A, but since the reaction and options are absent, there is no way to independently verify whether $A$ is correct.

Step 3: Conclusion

Because the question is incomplete, a step-by-step chemical solution cannot be produced.

Please provide the reaction image or the full reaction/options, and I can solve it properly.