How does an enzyme speed up a chemical reaction? enzymes:
a: lower the activation energy of chemical reactions.
b: raise the temperature of the cell, speeding chemical reactions.
c: store atp, allowing more energy to be used in chemical reactions.
d: act as a miniature “transfer trucks” gathering materials for chemical reactions and places them together.

The correct answer here is that lowers the activation energy of chemical reactions - A. 

By doing this, it essentially creates an environment where a chemical reaction can happen faster because it doesn't need as much energy to actually take place - for this reason it also happens more often as a lower energy treshold is usually reached faster than a higher one.