Umesh,
You are correct. This question could be formulated a bit better. But overall, the answer is still correct. In the explanation we say the following:
"[A is correct because...] Specification Limits (also known as tolerances) are the limits that your customer has given you. Since 15.2cm is within the customer specified tolerance you can deliver them without hesitation."
Answer C (adjust the process) may also be a valid option. Our original argument was that the first thing you do is to deliver the goods to the customer, then you adjust the process.
I'll make sure we rephrase answer C to make it clearer.