Final answer:
The variable that is a quantitative variable is 'Number of cars in a family'.
Step-by-step explanation:
Out of the given options, the variable that is a quantitative variable is C: Number of cars in a family. A quantitative variable is a type of variable that can be measured numerically, such as counting the number of cars in a family. In this case, the number of cars is a numerical value that can be counted, making it a quantitative variable.