用kill发送信号时的权限问题

forandom

man 2 kill:

For a process to have permission to send a signal it must either be privileged  (under  Linux:  have  the  CAP_KILL capability),  or the  real or effective user ID of the sending process must equal the real or saved set-user-ID of  the target process.  In the case of SIGCONT it suffices when the sending and receiving processes belong to the same  session.

对红色部分的理解，以下哪些情况用kill发送信号能成功？

A.  sender(ruid) == receiver(ruid) && sender(euid) == receiver(euid/set-user-ID)
B.  sender(ruid) == receiver(ruid) && sender(euid) != receiver(euid/set-user-ID)
C.  sender(ruid) != receiver(ruid) && sender(euid) == receiver(euid/set-user-ID)