active-passive

ACTIVE à PASSIVE

ACTIVE  sentences - the form is Present Perfect

          The Secretary is going to answer the letter.

PASSIVE  sentences – so it must to has been and  V3

          The letter has been answered by the secretary.

PASSIVE à ACTIVE

PASSIVE sentences – the form is Simple Present

          Medicine can be prescribed by a doctor.

ACTIVE  sentences – so it must to change the verb from V3 to V1

          A doctor can prescribe medicine.