What part of an enzyme determines its specificity?

The ACTIVE SITE determines the specificity of an enzyme. Only certain substrates can bind into the active site to form a product.
People often use lock and key mechanism to represent this process.
The keyhole of a lock is just as the active site, where only a key that fits in it can stick it in.
This represents the specificity, only that kind of key fits in. Only that kind of substrate can fit in the active site.

Idk