'A' promises that he saw 'B' at Lahore on a certain day. A is asked whether he himself was not in Calcutta that day. He attests to it. To show that A was at Calcutta on that day, evidence is offered—

• A. Evidence is not valid.
• B. The evidence will be admissible because the alleged fact that B was seen at Lahore on the day in question does not contradict it.
• C. The evidence is admissible because it refutes A as to a fact. which affects its credibility.
• D. This evidence is admissible not because he refutes 'A' as to a fact which affects his credibility, but because he refutes the alleged fact that 'B' was at Lahore on the day in question. Was seen.