हूँ only goes with मैं (first-person singular)
है goes with third-person singulars and तू (second-person informal)
हो goes with तुम (second-person intermediate formality)
हैं goes with third-person plurals, हम (first-person plural) and आप (second-person formal)
Can we have some consistency, please, Duolingo. One question I get wrong for not including "hain" at the end of a sentence ending "nahin aa rahe", then this one we are not even given "hain" as an option.