The book is rather highly priced, but so well worth ______ that it should be begged or borrowed rather than missed.

A．to read

B．to be read

C．reading

D．being read

一束光穿过介质1、2、3时，光路如图所示，则(    )

A．介质2的折射率最大

B．光线在介质2中的波长最长

C．光在介质3中的速度最大

D．入射光线到达时介质2和介质3的界面时，一定也发生反射