Which of the following are the assumptions involved in the auto-ignition theory put forth for the onset of knock in SI engines? 1. Flame velocity is normal before the onset of auto ignition. 2. A number of end-gas elements auto ignite simultaneously. 3. Preflame reactions are responsible for preparing the end-gas to ignite. Select the correct answer using the codes given below:

• A. 1 and 2            
• B. 1 and 3
• C. 2 and 3            
• D. 1, 2 and 3