Much of the criticism has focused on the railway’s online purchasing system which has been

问题补充：

Much of the criticism has focused on the railway’s online purchasing system，which has been

unable to the huge demand．

A. take notice of

B. attach importance to

C. show preference for

D. keep pace with

答案：

A. take notice of

B. attach importance to

C. show preference for

(答案→)D. keep pace with

解析：A．take notice of注意，B．attach importance to重视， C．show preference for偏爱， D．keep pace with跟上…的步伐，句意：很多批评是针对铁路的网上购买系统，这已经不能赶上巨大的需求。选D。