The correct answer is (d) Microencapsulation
To explain: Entrapment can be achieved by using microencapsulation. In this method entrapment, the enzyme is entrapped within a semipermeable membrane of a microcapsule and this is done by interfacial polymerization. In immobilization by adsorption, the enzyme is bound to suitable adsorbent which renders it immobile. In membrane confinement, the enzyme in aqueous solution is confined within a semipermeable membrane. In covalent binding, the enzyme is linked to the carrier matrix by covalent bond between them.