<span>When using active voice, the subject
performs the action noted by the main verb. (As one site put it, the
subject is a do-er or a be-er.)
When using the passive voice, the
subject is acted upon by another agent or an unknown something. (The
subjects of passive sentences are not do-ers or be-ers.)
These are much better explained with examples:
Active: Brutus stabbed Caesar. Passive: Caesar was stabbed by Brutus.
Active: The committee approved the new policy. Passive: <span>The policy was approved of by the committee.</span></span>
It is a compound sentence - a sentence that is composed of two simple (independent) sentences connected together -- in this case by the coordinating conjunction 'but.'
