The question refers to a molecule $(X)$ and four options, but in the provided prompt the structure of $(X)$ is missing and the option structures A, B, C, D are also not shown.

Because the reaction outcome with $\mathrm{HBr}(1\,\text{eq})$ depends completely on the actual structure of $(X)$, it is not possible to determine the major product uniquely from the text alone.

Step-by-step analysis

1. What is needed to solve this?
   For addition of $\mathrm{HBr}$, we must know:

   • whether $(X)$ contains an alkene, alkyne, alcohol, epoxide, diene, etc.
   • whether peroxides are present or absent
   • regiochemistry and possible rearrangements
   • the actual product choices

2. What is missing?

   • Structure of molecule $(X)$
   • Structures of options A, B, C, and D

3. Can the stored answer alone be trusted?
   The stored answer is given as A, but since the actual figures are absent, I cannot independently verify it from chemistry principles.

4. Conclusion
   With the information provided, the problem is incomplete. The answer cannot be derived rigorously unless the structure/image is supplied.

Comparison with stored correct answer

The stored correct answer is A, but due to missing structural information, I cannot truly confirm it by calculation or mechanism.

Please upload or type the structure of $(X)$ and the option structures so I can solve it properly.