• The preparation phase is also called a period of ignition lag.
• This is the first stage in the combustion stages in SI engines.
• According to the experiment, there is some time interval between the first spark given to the mixture (at point A) and the first flame appears out of the mixture.

The combustion process is usually described in terms of three distinct phases :

1. Ignition delay

2. Premixed combustion

3. Rate controlled combustion

Hence, the correct option is (A).