In a multi-channel cascade, how are the multi-channel usage priorities of the upper and lower MCUs allocated?

In a multi-channel cascade, how are the multi-channel usage priorities of the upper and lower MCUs allocated?
A . The two priorities are the same
B . The priority of the upper-level MCU is greater than that of the lower-level MCU.
C . The priority of the upper-level MCU is lower than that of the lower-level MCU.
D . You can configure the priority as needed

Answer: B