Correct Answer: Online activity classes for children are being held by the school.

Solution : The second option is the correct choice.

The passive voice is the voice in which the object experiences an action rather than the person who performs the action. Hence, the object in the active sentence becomes the subject in the passive voice.

The structure of the present continuous tense in passive form is: "Plural object + are being + past participle form of the main verb + by + agent of the action."

Hence, the correct answer is: " Online activity classes for children are being held by the school ."