Which of the following can affect the activity of an enzyme?
1. activation energy, reactants, and ph
2. proteins, regulatory molecules, and ph
3. temperature, ph, and regulatory molecules
4. temperature, lipids, and activation energy

The correct option is 3.
Enzymes are biological catalysts which speed up the rate of biochemical reactions inside the cells. Enzymes are very specific in action and they require specific conditions called optimum conditions for them to function optimally.
When the optimum conditions are not met, an enzyme's activity will be lowered or totally stopped.
Conditions that affect the optimum activity of an enzyme include: temperature, pH level and regulatory activity of regulatory enzymes and hormones.