1. The natural numbers are those that are used for counting. Natural numbers cannot be negative.
2. A whole number is a member of the set {0,1, 2, 3, …} - this set is the set of natural numbers with zero. Whole numbers cannot be negative.
3. Integers include whole numbers and negative whole numbers. Integers can be positive, negative, or zero.
4. Real numbers include:
- natural numbers;
- whole numbers;
- integers;
- rational numbers;
- irrational numbers.
Real Numbers can also be positive, negative or zero.
Consider number -1.2. It is negative, then options 1 and 2 are wrong. Also option 3 is false, because 1.2 is not natural number (cannot be used for counting), then -1.2 is not integer. Number -1.2 is real number.
Answer: correct choice is D.