The correct option is A apoenzyme
Substances which can be destroyed or deactivated by heat are called thermolabile substances. Proteins get denatured at high temperatures. The protein part of the enzyme is called apoenzyme. Thus the thermolabile protein part of enzyme is apoenzyme.
The non protein part of an enzyme is called cofactor. The apoenzyme and cofactor together are called holoenzymes.
Enzymes whose amino acid sequence or structure varies but they catalyse the same reaction are called isoenzymes.
The inactive precursor of an enzyme is known as proenzyme.