In Canada,you Are a Party to a Crime and Liable

In Canada,you are a party to a crime and liable for conviction for murder in all of the following circumstances except one.Which is the exception?

A) You plan a murder with others,but change your mind and tell the others you do not want any part of it,but they go ahead and commit the murder anyway.
B) You counsel the commission of murder with another person who actually commits it.
C) You plan and commit a robbery,but during it,without your knowledge,your accomplice kills a guard.
D) You help another person commit murder.