China began selling tickets for the Wuhan-Guangzhou high-speed railway, ______ boasts the world's fastest train journey with a 350km per hour average speed.

1. A.
   which
2. B.
   that
3. C.
   it
4. D.
   what

China began selling tickets for the Wuhan-Guangzhou high-speed railway, ______ boasts the world's fastest train journey with a 350km per hour average speed.  

       A. which              B. that                   C. it                     D. what     

China began selling tickets for the Wuhan-Guangzhou high-speed railway, ______ boasts the world's fastest train journey with a 350km per hour average speed．

A．which                    B．that                C．it            D．what