Suppose you are Wangwei in the dialogues, read carefully Dialogues 3-5 and choose which answer may mark (标志着) a participant(参会者) in a trade fair is possible to become your potential customer.
A. When a participant asks for your catalog
B. When a participant asks for your name card
C. When a participant asks about quality, price and discount of your product
D. When a participant greets you