Refer to the exhibit. 
Why is the neighbor relationship between R2 and R4 shown as ES-IS?
A.
because there is an MTU mismatch between R2 and R4
B.
because interface S3/0 of R4 is configured as L1/L2
C.
because interface S3/0 of R2 is configured as L1
D.
because there is a hello interval mismatch between R2 and R4
A.
because there is an MTU mismatch between R2 and R4
Whenever the MTU is mismatch b/w 2 ISIS neigbours it will show this status