Question

the active site of an enzyme is the region that...
binds allosteric regulators of the enzyme.
binds substrates for the enzyme.
binds noncompetitive inhibitors of the enzyme.
is blocked by the presence of a coenzyme or a cofactor.

Explanation:

Enzymes are biological catalysts. The active site is a specific region on the enzyme. Allosteric regulators bind to allosteric sites (not the active site). Non - competitive inhibitors bind to a site other than the active site. Coenzymes and cofactors usually assist the enzyme at the active site (they do not block it). Substrates are the reactants that the enzyme acts on, and they bind to the active site of the enzyme.

Answer:

binds substrates for the enzyme.