The country's railway system has launched online ticket-booking and a real-name ticket purchasing system, and requires passengers to provide their ID numbers when buying tickets.
A. which
B. that
C. what
D. this
网友回答
A. which
(答案→)B. that
C. what
D. this
解析：本题考查代词。题干中and已是连词，不要其它连词。此处that是代词，用来指代前面句子的内容。