The question as provided is incomplete.

1. What is missing?

The prompt says:

'A' and 'B' in the following reactions are :

but the actual reaction scheme/structures are not shown, and even the options A, B, C, D are empty.

So the essential information needed to solve the problem is missing:

• the starting compound(s),
• reagents/conditions,
• products/intermediates labeled $A$ and $B$,
• the actual option choices.

2. Why the answer cannot be derived

In organic chemistry, identifying compounds $A$ and $B$ depends entirely on the reaction sequence. Without the reaction pathway, there is no chemically valid way to determine them.

Therefore, a step-by-step solution cannot be performed from the given data.

3. Comparison with stored correct answer

The stored correct answer is D, but since the reaction scheme and options are missing, I cannot independently verify whether option $D$ is correct.

So I do not have enough information to agree with the stored answer.

4. What is needed to solve it

Please provide:

1. the full reaction diagram/image,
2. all reagents and products,
3. the complete option list.

Then I can solve it systematically and verify the correct option.