__________ have covered all high-speed and intercity railways on the mainland China by April 2020 and then expanded to conventional speed railways in June 2020. 到2020年4月, __________已覆盖中国大陆所有高铁和城际铁路，并于2020年6月扩大到普速铁路。
A、single-trip ticket 单程票
B、e-ticket 电子客票
C、paper ticket 纸质票