Explanation
A stack master retains its role unless one of these events occurs: + The switch stack is reset.* + The stack master is removed from the switch stack. + or powered off -> Answer C is correct.
+ The stack master fails. + The switch stack membership is increased by adding powered-on standalone switches or switch stacks.* In the events marked by an asterisk (*), the current stack master might be reelected based on the listed factors.
Reference:
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3650/software/release/3e/ha_stack_manager/configu