The correct choice is (d) proenzyme
To elaborate: Enzymes that are present in inactive and need to cleaved in order to be activated are referred to as proenzyme. This is also called as zymogen. Additional non protein group in an enzyme required for its optimal activity is referred to as cofactors. Complex organic or metallo-organic compound in an enzyme is called coenzyme. Two or more enzymes with identical function but the different structure is referred to as isoenzyme.