The correct answer is option Their shapes fit snugly together.
The active site of the enzyme is designed in such a way that is can comfortable get attached to the substrates. The substrate recognizes the active site of the enzyme and get fits into it. The attachment of the enzyme and the substrate is well explained by the lock and key mechanism, which suggest that the enzymes and the substrate are similar to the lock and key. every lock has its unique key and vice versa, similarly, every enzyme has its own substrate and vice versa.
