Which of the Following Observations Is an Example of a Positive

Which of the following observations is an example of a positive correlation?

A) When a population's intake of plant foods decreases,the percentage of obese people in that population increases.
B) When a population's vitamin D intake decreases,the percentage of people in the population that have healthy immune systems decreases.
C) When a population's level of vitamin C in white blood cells increases,the percentage of people in the population who develop scurvy decreases.
D) When a population's level of physical activity increases,the percentage of people who develop heart disease decreases.