Choose the option that is the active form of the sentence.

By whom was this window broken? Five packets of milk were delivered by the milkman.

Who broke this window? The milkman delivered five packets of milk.

The correct option that is the active form of the sentence is Who broke this window? The milkman delivered five packets of milk.

The other options are incorrect because:

• Who is breaking this window? is in the present progressive tense, while the original sentence is in the past tense.
• Whom was break this window? and Who had broke this window? are grammatically incorrect. The verb "to break" is followed by a direct object, but the phrases "whom was break" and "who had broke" are not direct objects.