Which of the following expressions is a polynomial in one variable ?

Which of the following expression is a polynomial?

State which of the following expressions are a polynomial in one variable and which are not : x^(3) + y^(3) + z^(3) - 3xyz

State which of the following expressions are a polynomial in one variable and which are not : 5x^(2) - 3x + 7

State which of the following expressions are a polynomial in one variable and which are not : 7t^(2) - 5t +3

State which of the following expressions are a polynomial in one variable and which are not : 16x^(2) - 49y^(2)

State which of the following expressions are a polynomial in one variable and which are not : sqrt(7)x^(3) + (5)/(3)x^(2) - 9x + 17

Which of the following expressions are polynomials in one variable and which are not? State reasons for your answer:- y^2+sqrt2