A _____________ can be purchased at any ticket booths set at these metro stations at a relatively cheap price, normally about CNY 20. 在这些地铁站的任何一个售票亭都可以以相对便宜的价格购买___________，通常是20元左右。
A、round-trip ticket 往返票
B、one-day travel pass 一日票
C、one-week travel pass 一周票