## Core Concept
The question pertains to the concept of **epidemiology**, specifically the measurement of disease occurrence in a population. **Incidence** and **prevalence** are key terms used to describe the frequency of diseases. Incidence refers to the number of new cases that develop in a specified time period among a population at risk, while prevalence refers to the total number of cases of a disease present in a population at a given time.

## Why the Correct Answer is Right
The correct answer, **C. Incidence**, is right because an increase in new cases directly reflects an increase in the **incidence** of a disease. Incidence specifically measures the rate of occurrence of new cases of a disease in a population over a specified period. Therefore, when there is an increase in new cases, it indicates a higher incidence rate, suggesting that more individuals are being affected by the disease over time.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because **Prevalence** refers to the total number of cases (new and existing) of a disease in a population at a given time. An increase in prevalence could be due to an increase in new cases (incidence), a decrease in the number of people recovering or dying from the disease, or both.
- **Option B:** This option might seem related but is not directly relevant to the question about new cases. **Morbidity** refers to the condition of being diseased, and while related, it does not specifically denote the rate of new cases.
- **Option D:** **Mortality** refers to the rate of death in a population. While mortality rates can provide insights into the severity of a disease, an increase in new cases specifically relates to incidence, not mortality.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **incidence** is a measure of the risk of developing a disease, and an **increase in incidence** indicates a growing health problem within a community. This concept is crucial for public health planning, resource allocation, and intervention strategies.

## Correct Answer: C. Incidence.