Choice A rationale:

Hoarseness of voice can be a symptom of an allergic reaction, indicating swelling and inflammation in the throat. If the client’s voice is no longer hoarse after taking diphenhydramine, it suggests that the medication has been effective in reducing this symptom.

Choice B rationale:

Diphenhydramine is an antihistamine and can often cause drowsiness as a side effect. Therefore, feeling more alert would not typically indicate that the medication has been effective.

Choice C rationale:

While headaches can sometimes be associated with allergic reactions, they are not a primary symptom that diphenhydramine targets. Therefore, absence of a headache does not necessarily indicate effectiveness of the medication.

Choice D rationale:

Increased appetite is not typically associated with the effectiveness of diphenhydramine in treating allergic reactions.