I could use some help! 30 points! An investigation is carried out into the effect of temperature on the activity of lipase. Separate tubes of substrate solution and enzyme solution are left in temperature-controlled water baths for ten minutes before mixing. Why is this done?

A- To activate the enzyme.
B-To allow time for the enzyme and the substrate to react.
C- To control the independent variable.
D- To keep a standardized variable constant.

Help is always appreciated, thank you!