In an automatic gearbox, what is a driver required to do before shifting from the P gear to any other gear?

1. Correct answer: Apply the brakes firmly.
2. Step firmly on the accelerator.
3. Step firmly on the clutch pedal.
4. Step on the brake and the clutch pedals simultaneously. And then shift to the required gear.

WhyBefore moving an automatic's selector out of P, press the brake firmly.