Change the given sentence into its passive voice.
It had had it.
This question looks odd at first because the sentence "It had had it" repeats the word "had" twice, but it is simply the past perfect tense of "it has it," meaning "it possessed it before some other past event." The task is to turn this into the passive voice correctly.
Remember the general rule for past perfect passive: Object + had been + past participle + by + Subject. Applying this to "It (subject) had had (verb) it (object)" gives us "It (new subject) had been had (participle) by it (original subject)."
Let's summarize:
The correct passive form is "It had been had by it," which is option (b).