Could be false. We know that histamine doesn’t play role in how colds produce symptoms. But what causes colds? We don’t know that pollens and allergens don’t cause colds.

Could be false. We don’t know what’s more difficult to treat. Although antihistamines can reduce allergy symptoms, that doesn’t mean allergies are easier to treat than colds. Maybe antihistamines can also reduce cold symptoms, or there are other things that can treat colds.

Could be false. We were told antihistamines have “other effects.” Those effects might include reducing cold symptoms; we don’t know. Although histamines aren’t part of cold symptoms, antihistamines might still reduce those symptoms through some means besides blocking histamines.

Could be false. We don’t know whether antihistamines can “effectively treat” sleeplessness. Although antihistamines can cause drowsiness, that doesn’t guarantee that they can treat sleeplessness.

Must be true. Histamines play no role in how colds produce symptoms. So, if antihistamines can reduce cold symptoms, it won’t be through blocking histamines. It would be through some other mechanism that’s related to producing cold symptoms.