**Core Concept**
The Schick test is a method used to determine an individual's susceptibility to diphtheria, a bacterial infection caused by Corynebacterium diphtheriae. It assesses the presence of circulating antibodies against diphtheria toxin, which protects against the disease. The test involves injecting a small amount of diphtheria toxin or a toxoid (inactivated toxin) into the skin.

**Why the Correct Answer is Right**
A positive Schick test indicates that the individual lacks sufficient antibodies against diphtheria toxin, making them susceptible to the disease. This is because the toxin causes a localized skin reaction, indicating that the person's immune system is unable to neutralize the toxin. The lack of circulating antibodies suggests that the person has not been previously exposed to or immunized against diphtheria.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the outcome of a positive Schick test. A positive test indicates susceptibility, not immunity.

**Option B:** This option is incorrect because it is the opposite of the correct answer. A negative Schick test indicates that the individual has sufficient antibodies against diphtheria toxin.

**Option C:** This option is incorrect because it does not accurately describe the outcome of a positive Schick test. A positive test does not indicate that the individual is resistant to diphtheria.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the Schick test is no longer commonly used due to the widespread availability of diphtheria toxoid vaccines.

**Correct Answer:** D. The person is susceptible to diphtheria.