what happens to the enzyme after an enzymatic reaction is complete? A) it loses a carbon atom B) it gains a water molecule C) it loses its hydrogen atom D) nothing happenes

The Option D is correct.

After enzymatic reaction, nothing happens with enzyme and it remain unchanged.

During an enzyme catalyzed reaction the enzyme bonds with a specific substrate at the active site. This is called an enzyme-substrate complex. The substrate is converted into a specific product, but the enzyme remains unchanged. Enzymes accelerate reactions by factors of at least a million.