answer: Bob meets Mary in Boston. Bob comes to visit his grandparents, while Mary comes to attend Carol's wedding.
documents: #Person1#: Hi, Mary, you are in Boston, too. I remember you are admitted to Washington University. And are you meeting someone at the airport?
  #Person2#: Glad to meet you here, Bob. I am meeting my parents. You are paying a visit to your grandparents?
  #Person1#: Right, have you graduated from the university?
  #Person2#: No, I will graduate next year. My sister Carol will get married this weekend, so I come here to attend her wedding.
  #Person1#: How time flies! I haven't seen her for years.