Answer:
C. rational numbers and irrational numbers
Explanation:
Rational numbers are those numbers that can be used to express the ratio of two whole numbers. An example is the figure 2. It can be expressed as a fraction of another number like when we write 2/8. Both figures are rational. Irrational numbers cannot be used to express the ratio of two whole numbers or integers. An example is a digit like 0.666666... Rational and irrational numbers are real numbers because real numbers encompass all the types of numbers we can think of, positive, negative, decimals, whole, etc.
The density of numbers is seen in the fact that there is no vacuum created between real numbers when plotted on the number line.