The argument is concerned with whether or not doctors are required for accurate diagnosis of swimmer’s ear. The argument is not concerned with severity of infections, so this information does not weaken the argument.

(B) provides information about the 16% who made an incorrect self-diagnosis of swimmer’s ear. The argument is about the high rate of accurate self-diagnosis, so this information does not weaken the argument.

This information attacks the argument’s key assumption that, because of the high rate of accurate self-diagnosis, most people can diagnose themselves without ever seeing a doctor. (C) says that previous visits to a doctor may have informed these accurate self-diagnoses.

This does not change the fact that self-diagnoses are more accurate than doctors’ diagnoses in general. The key support for the argument is that self-diagnoses are highly accurate. (D) does not weaken the argument that most people can self diagnose without ever seeing a doctor.

The argument is concerned with diagnosis, not treatment, of swimmer’s ear.