Question NA343

[glhart]

On Question NA343, why is there both a "CSU/DSU" box AND an "Analog Modem"?  It seems like the green box would be the CSU/DSU and the line going from the green box to the WAN would be a Digital Line (aka Serial link).  There is no explanation for this question.  Adding an explanation as to why this is the way it is would be really helpful.  If this is a real question on the test, I would not know why I am putting this as the answer.

Thank you,
Geoff