Chapter 4 - Polynomials - 4.3 Polynomials - 4.3 Exercise Set - Page 251: 8

The answer is $\color{red}{c) \dfrac{3}{x} - 6x^2 + 9}$.

Remember that a trinomial consists of three monomials. In this item, an expression with three terms but not a trinomial is $\dfrac{3}{x} - 6x^2 + 9$, since $\dfrac{3}{x}$ is not considered to be a monomial. The answer is $\color{red}{c) \dfrac{3}{x} - 6x^2 + 9}$.