A spontaneous process is defined as a process which

• In thermodynamics, a spontaneous process is a process which occurs without any external input to the system. A more technical definition is the time-evolution of a system in which it releases free energy, and it moves to a lower, more thermodynamically stable energy state (closer to thermodynamic equilibrium).
• A spontaneous process may take place on its own or by initiation;
• It need not be instantaneous always 

Hence the correct answer is (B) takes place by itself.