Choose the correct option to change the given sentence from Active Voice to Passive Voice:

They cancelled all flights because of fog.

All flights were cancelled because of fog.

The reason option (1) is the correct choice to change the given sentence from active voice to passive voice is because it follows the standard passive voice construction in English.

In a passive construction, the subject of the active sentence ("They" in this case) becomes the agent of the action and is preceded by the verb "were cancelled." The object of the active sentence ("all flights" in this case) becomes the new subject in the passive sentence, and the original verb is changed to its past participle form ("cancelled”).