Correct Answer: Books can be bought online from Amazon.

Solution : The third option is the correct choice.

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 passive voice structure for modal verbs is as follows:

Subject + modal verb + be + past participle + rest of the phrase.

Therefore, the correct passive voice transformation is: "Books can be bought online from Amazon."