## Core Concept
The sensitivity of a screening test is a measure of its ability to correctly identify those with the disease, calculated as the number of true positives (those correctly identified as having the disease) divided by the total number of actual cases (as determined by the gold standard test). In this context, it reflects how well the screening test can detect diabetes compared to the gold standard.

## Why the Correct Answer is Right
To calculate the sensitivity of the screening test, we need to know the number of true positives (those with diabetes who tested positive on the screening test) and the total number of actual cases of diabetes as per the gold standard test. Given that the screening test showed 90 positives and the gold standard test showed 100 positives, we assume the 90 positives from the screening test are true positives (though in real scenarios, there could be false positives among them). The gold standard test identified 100 individuals with diabetes. Therefore, the sensitivity of the screening test is 90/100 or 0.9.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because without calculation, we cannot assume it is right; the correct calculation yields a sensitivity of 90%, making this option potentially incorrect based on the actual numbers provided.
- **Option B:** Similarly, this option would be incorrect if it does not match the calculation of 90%, which is the correct sensitivity based on the provided numbers.
- **Option D:** This option is incorrect because, based on our calculation, the sensitivity is 90%, not the value presented in this option.

## Clinical Pearl / High-Yield Fact
A key point to remember is that sensitivity and specificity are crucial characteristics of a diagnostic test. Sensitivity is the test's ability to correctly identify those with the disease (true positive rate), while specificity is its ability to correctly identify those without the disease (true negative rate). For screening tests, especially in populations with a high risk of disease, a high sensitivity is often desired to catch as many cases as possible.

## Correct Answer: B. 0.9