(2013·沈阳重点中学协作体高三预测)I just wonder ________ that makes him so excited.

A．why it is

B．what is it

C．how it is

D．what it is

锚网索支护巷道掘进过程中，够间排距应及时打设锚杆、锚索，锚索线外露长度为200mm，锚杆外露长度为（）。