In the Tuberculin Skin Test, What Would Be the Most

In the tuberculin skin test, what would be the most likely reason why a positive test would NOT necessarily indicate an infection in progress in a patient in the United States?

A) False positives occur all the time. This might simply be an example of that.
B) The TB skin test is a measure of reactivation of memory T cells. The memory T cells would be formed either during an active infection or would be remnants of a prior infection that may be cleared. Since the memory of the response persists, the test still shows positive, even though the patient is cleared of actual infection.
C) Each person in the US receives the BCG tuberculosis vaccine. This is an attenuated mycobacterium vaccine. The response to this vaccine makes us positive for the TB skin test, even though we may not have actually had a TB infection at any point in our lives.
D) This is a trick question-a positive TB skin test ALWAYS indicates a current, active infection.