Question

Lightning had knocked down several trees. Change into passive voice

Answer 1

The given sentence can be changed into active voice as shown and explained below:

Several trees had been knocked down by lightning.

The verb in the sentence was in Past Perfect active voice form (had knocked down). When we convert the active voice of Past Perfect into passive, we use passive form equivalent to the active form. The passive form in Past Perfect is had been+V3.  The object is made the subject and vice versa; and 'by' is added.

Answer 2

Answer:

SEVERAL TREES HAD BEEN KNOCKED FOWN BY LIGHTNING...