**Core Concept**
The sensitivity of a diagnostic test measures its ability to correctly identify those with the disease (true positive rate). It is calculated as the number of true positives divided by the sum of true positives and false negatives.

**Why the Correct Answer is Right**
To calculate the sensitivity, we need to identify the true positives (diseased individuals who test positive) and false negatives (diseased individuals who test negative). From the table, there are 40 true positives (Present +ve) and 10 false negatives (Present -ve). The sensitivity is calculated as the number of true positives divided by the sum of true positives and false negatives: (40 / (40 + 10)) = 80%.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not correctly calculate the sensitivity. The formula for sensitivity is (true positives) / (true positives + false negatives), not (true positives) / (true positives + false positives).

**Option B:** This option is incorrect because it is the formula for specificity, not sensitivity. Specificity measures the ability of a test to correctly identify those without the disease.

**Option C:** This option is incorrect because it is the formula for positive predictive value, not sensitivity. Positive predictive value measures the probability that a positive test result is true.

**Option D:** This option is incorrect because it is not a valid formula for calculating sensitivity.

**Clinical Pearl / High-Yield Fact**
Remember, sensitivity is a measure of the test's ability to detect those with the disease, while specificity measures the test's ability to exclude those without the disease.

**Correct Answer:** B. 80%.