A very sudden rise in pressure during combustion accompanied by a metallic, hammer like sound is called knocking of the unit or detonation and usually occurs (16)

(a) Near the end of the pressure rise after ignition of fuel charge

(b) Just before the fuel charge is about to ignite

(c) Immediately after the unit reaches peak pressure and before ignition of fuel

(d) At any stage of the combustion process.

State the correct answer and explain why the other reasons given are not justified.