Question

the reactants of a chemical reaction that fit in the active site of the enzyme.
options (from image): lactose, how do enzymes speed up chemical reactions?, substrate, reusable

Explanation:

The question is about the term for reactants in a chemical reaction that fit into an enzyme's active site. Lactose is a specific sugar (a substrate for lactase), "How do enzymes speed up..." is a question, "Reusable" refers to enzyme property. The correct term is "Substrate" as substrates are the reactants that bind to enzyme active sites.

Answer:

Substrate