**Core Concept**
The case fatality rate (CFR) is a measure of the severity of a disease, calculated as the proportion of deaths among the total number of cases. In the context of an outbreak, CFR helps in assessing the virulence and potential impact of the disease.

**Why the Correct Answer is Right**
To calculate CFR, we divide the number of deaths by the total number of cases and multiply by 100 to get the percentage. In this outbreak, there were 5 deaths among 20 cases. Therefore, the CFR is calculated as (5/20) x 100 = 25%. This means that 25% of the cases resulted in death.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not provide a valid calculation for CFR.
* **Option B:** This option is incorrect because it does not take into account the total number of cases in the calculation.
* **Option C:** This option is incorrect because it does not provide a valid percentage value for CFR.

**Clinical Pearl / High-Yield Fact**
CFR is an important epidemiological parameter that helps in assessing the severity of a disease outbreak. It is essential to calculate CFR accurately to develop effective public health strategies for controlling the spread of the disease.

**Correct Answer:** A. 25%.