**Core Concept**
The concept of sensitivity in medical testing refers to the proportion of true positive results among all actual positives in a population. It measures a test's ability to correctly identify individuals with a particular disease or condition.

**Why the Correct Answer is Right**
A test with a sensitivity of 90% means that out of 100 individuals who actually have the disease, the test will correctly identify 90 of them as positive. This is because the test is able to detect 90% of the true positives. In other words, the test is highly specific in identifying individuals with the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the sensitivity of 90% does not imply that the test will correctly identify 90% of individuals without the disease (specificity).
**Option B:** This option is incorrect because the sensitivity of 90% does not indicate the test's ability to detect the disease in a high-risk population.
**Option C:** This option is incorrect because the sensitivity of 90% does not imply that the test will correctly identify 90% of individuals with a different disease or condition.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that a high sensitivity test is not necessarily a high specificity test, and vice versa. Therefore, it's crucial to evaluate both sensitivity and specificity when interpreting the results of a medical test.

**Correct Answer: C. It means that the test will correctly identify 90% of individuals with the disease.**