When adding device pairs to an SRDF/Metro configuration using the -exempt option, what prevents a device pair from being added?

When adding device pairs to an SRDF/Metro configuration using the -exempt option, what prevents a device pair from being added?
A . R2 device is larger than the R1 device
B . Source group and device pair are in SRDF/S mode
C . R1 device is the source of a TimeFinder data copy
D . Source group and device pair are in SRDF/Adaptive Copy mode

Answer: A