Final answer:
In the quadratic expression 15x²+2x+9, the constant term is 9, which corresponds to answer choice D.
Step-by-step explanation:
The question asks to identify a constant from the given quadratic expression 15x²+2x+9. In a quadratic expression of the form ax² + bx + c, the constant is the term without the variable, which is 'c'. Therefore, from the provided options, the constant in the expression is 9, which corresponds to answer choice D.