Which of the following can be a characteristic of rational numbers?

Rational numbers are defined as numbers that can be expressed as the quotient of two integers, where the denominator is not zero. This means that any integer, such as negative and positive integers, is a rational number because it can be expressed as itself divided by one (e.g., 5 can be written as 5/1, and -3 can be written as -3/1). Therefore, the characteristic that rational numbers can be positive or negative integers aligns correctly with the definition of rational numbers.

The other options do not accurately represent characteristics of rational numbers. For instance, rational numbers can indeed be expressed as fractions, which contradicts the first option. The second option inaccurately limits rational numbers to just whole numbers and excludes decimals, which are also rational as long as they can be represented as fractions (e.g., 0.5 is 1/2). The fourth option incorrectly asserts that rational numbers include only prime numbers, which is also false as many rational numbers could be composite or even negative and not necessarily prime.