For expression to be polynomial all the exponent must be non negative.
For first option,
[tex]\frac{2}{x}-8y=2x^{-1}-8y[/tex]
It is not a polynomial expression.
For second option
[tex]3x^2-7y[/tex]
No negative exponent, so it is polynomial equation.
For third option,
[tex]4x^2-9[/tex]
No negative exponent, so it is polynomial equation.
For fourth option,
[tex]3x^{-2}+y^3[/tex]
It is not a polynomial expression.
So option B and C is correct option.
