The set of numbers that is always rational is integers.
Rational numbers are defined as numbers that can be expressed as the quotient of two integers (where the denominator is not zero). Integers (like -2, 0, 1, 7) can be expressed as a fraction, for example, -2 can be written as -2/1, which makes them rational.
While negative numbers and positive numbers can include irrational numbers (like -√2 or √2), integers are a specific subset of rational numbers that always maintain the criteria for being rational.
Decimals can be rational or irrational (e.g., 0.5 is rational, while 0.333... (which is 1/3) is rational, but numbers like π (3.14...) are irrational).
Therefore, out of the options listed, integers are the correct answer.