A rational function is defined as the ratio of two polynomials:
\[
f(x) = \frac{p(x)}{q(x)}
\]
Polynomials are continuous everywhere, and the quotient of two continuous functions is also continuous at every point where the denominator is not zero. Therefore, a rational function is continuous at all \(x\) where it is defined (i.e., where \(q(x) \ne 0\)).
So, the assertion is true.
The reason correctly explains this: the structure of a rational function (being a quotient of polynomials) guarantees continuity at all defined points.