The protective covering that is not made of cells on the outside of a roundworm is called

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme

it's not c. i took the quiz and got it wrong. so my best guess is b.

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