Final answer:
The expressions that are polynomials in the given options are: 3x² - 7y and 4x² - 9.
Step-by-step explanation:
A polynomial is a mathematical expression that consists of variables, coefficients, and exponents. The exponents must be non-negative integers. Therefore, the expressions that are polynomials in the given options are:
- 3x² - 7y
- 4x² - 9