Which two substances bind using a lock-and-key mechanism?

enzyme and substrate

reactant and substrate

substrate and product

reactant and product

It would be A: enzyme and substrate

The answer is the first option. Enzyme and substrate bind using a lock-and-key mechanism. Enzymes act on a specific substrate and a substrate needs a specific enzyme, this is what is called a lock-and-key mechanism. Enzymes and substtates are like a key and a lock, one is for each other.