A sample of breakfast cereals was classified as either a hot or cold cereal. In addition, the number of calories/serving and grams of fat/serving (integer values) were measured. It was also recorded whether each cereal meets the daily nutritional requirements for iron, using the following scale: 0 = does not meet daily nutritional requirements for iron; 1 = meets not more than 25% of daily nutritional requirements for iron; 2 = meets more than 25% of daily nutritional requirements for iron. Which of the following is correct?

a. The number of calories/serving is a quantitative variable.
b. The measurement of "meets daily nutritional requirements for iron" is a quantitative variable.
c. The variable "hot/cold" is a quantitative variable.
d. The variable "grams of fat" is a categorical variable.