**Core Concept:** Odd's ratio is a measure of the association between an exposure (in this case, smoking) and an outcome (disease development). It helps determine the strength of association and the relative risk.

**Why the Correct Answer is Right:**

In this scenario, we have two groups: smokers and non-smokers. The number of cases (disease development) and the total number of subjects in each group are given. We can calculate the odd's ratio using the formula:

Odds Ratio (OR) = [(Number of cases in exposed group) / (Number of cases in unexposed group)] / [(Number of subjects in exposed group) / (Number of subjects in unexposed group)]

In this case:
Number of cases in exposed group (smokers): 30
Number of cases in unexposed group (non-smokers): 10
Number of subjects in exposed group: 50 (smokers)
Number of subjects in unexposed group: 50 (non-smokers)

So, the calculation would be:
OR = (30/10) / (50/50) = 3

The correct answer is:
**Correct Answer: C. 3**

**Why Each Wrong Option is Incorrect:**

A. This option is incorrect because the correct answer is given as a whole number (3) and not a fraction or decimal.

B. This option is incorrect because it doesn't represent the calculated odds ratio (3).

D. This option is incorrect because it doesn't represent the calculated odds ratio (3).

**Why the Correct Answer is Right:**

The odds ratio (OR) is a measure of the strength of association between smoking and the disease risk. A value greater than 1 indicates increased risk, and a value equal to or greater than 3 indicates a strong association. In this case, an OR of 3 suggests that smokers have a 3x greater risk of developing the disease compared to non-smokers.

**Clinical Pearl:**

The findings from this study indicate that smoking is a strong risk factor for disease development. This information is crucial for healthcare professionals to counsel patients on the risks associated with smoking and promote smoking cessation strategies to prevent disease occurrence.

Understanding odds ratios can provide valuable insights into the strength of an association between a risk factor (smoking) and an outcome (disease development). A higher odds ratio indicates a stronger association, which in this case is 3, suggesting a strong relationship between smoking and the disease.