Help me answer this chemistry question. thank you!

A. Inflation pressure of the tyres

Explanation:

In an experiment, the independent variable is the variable that the experimenter changes or manipulates in order to induce a response in another variable called Dependent variable.

In this case in which an experiment was conducted on how inflation pressure of tyre affects a vehicle's maximum speed. The tyres of three different vans were used. The tyre of the first van were set at normal pressure of 35psi, the other van tyres were set at 40psi (overinflated) and 30psi (underinflated) respectively. This means that the INFLATION PRESSURES OF THE TYRES were the variable being changed, hence, is the INDEPENDENT VARIABLE.

the answer is option a.