The optimizes airflow, keeps cylinder pressure in a certain range, and determines the engine's operating range

Valve timing determines how much, how long, and when the valves open. Since the valves allow the air-fuel mixture into the engine, these factors affect horsepower and torque. The valve timing determines the engine’s operating range, optimizes airflow, and keeps cylinder pressure in a certain range.

You forgot to add the possibilities. we don't know the options from which to choose.