What layer of the OSI model would you assume the problem is in if you type show interface serial 1 and receive the following message? \"Serial1 is down, line protocol is down.\"

What layer of the OSI model would you assume the problem is in if you

1.	What layer of the OSI model would you assume the problem is in if you type show interface serial 1 and receive the following message? \"Serial1 is down, line protocol is down.\"
A.	Data Link layer
B.	Physical layer
C.	None. It is a router problem.
D.	Network layer
Answer» C. None. It is a router problem.