Which of the following statements about rational numbers is true?

Rational numbers are defined as numbers that can be expressed as the quotient of two integers, where the denominator is not zero. This definition encompasses both fractions and whole numbers (which can be represented as fractions with a denominator of 1). Therefore, the statement that rational numbers can include fractions and integers is accurate, as it highlights that any integer (like -3 or 5) can be written as a fraction (-3/1 or 5/1) and that fractions themselves (like 1/2 or 3/4) are also rational numbers.

The other statements are incorrect for the following reasons: Not all rational numbers are whole numbers since whole numbers only include non-negative integers, while rational numbers also include fractions and negative integers. Additionally, rational numbers can indeed include negative values, as evidenced by integers like -1 or fractions like -1/2. Lastly, rational numbers cannot be irrational; they occupy distinct categories in the number system — rationality and irrationality are mutually exclusive. Thus, the clarity of definition supporting the inclusion of both fractions and integers makes the correct answer valid.