Final answer:
Conjunctivitis typically spreads to the opposite eye due to its contagious nature, especially in cases of viral and bacterial conjunctivitis, while allergic conjunctivitis is not contagious.
Step-by-step explanation:
The correct statement regarding conjunctivitis is d) conjunctivitis usually spreads to the opposite eye. This is because conjunctivitis, particularly viral conjunctivitis, is contagious and can easily spread from one eye to the other eye or to other individuals through contact with eye discharge. Bacterial conjunctivitis is also very contagious, being transmitted via secretions from infected individuals. However, allergic conjunctivitis is not contagious as it is caused by allergens, not by infectious agents. It is important to understand that treatments vary; for example, antibiotic treatment is ineffective against viral conjunctivitis, which typically resolves on its own, while bacterial conjunctivitis may be treated with topical antibiotics to prevent the spread and hasten recovery.