谁帮我看一下CCNA的这个题?后面的几个选项我不懂是什么意思呀!

谁帮我看一下CCNA的这个题?后面的几个选项我不懂是什么意思呀!
As a network administrator,you will need to decide on the appropriate network
devices to use.Which of the following correctly describes the roles of devices in a
WAN?(Choose three)
A.A CSU/DSU terminates a digital local loop.
B.A router is commonly considered a DCE device.
C.A modem terminates an analog local loop.
D.A router is commonly considered a DTE device.
E.A modem terminates a digital local loop.
F.A CSU/DSU terminates an analog local loop.
G.A modem is used to terminate a T1