What is the best course of action to take?

After implementation of the product, the customer reports defects.

What is the best course of action to take?
A . Do nothing since the solution is now the responsibility of the operations manager.
B . Compare reported defects with user acceptance test results.
C . Involve the end users and plan a new round of acceptance tests to check the gaps.
D . Escalate the issue to the project manager since the acceptance was given by the customer.

Answer: B