Which SRDF mode pairing is unsupported in a Concurrent SRDF solution?

Refer to the exhibit.

Which SRDF mode pairing is unsupported in a Concurrent SRDF solution?

A.
Leg 1: Synchronous
Leg 2: Asynchronous

B.
Leg 1: Asynchronous
Leg 2: Asynchronous

C.
Leg 1: Synchronous
Leg 2: Synchronous

D.
Leg 1: Synchronous
Leg 2: Adaptive Copy Disk