Which of the following expressions are polynomials in one variable and which are not? State reasons for your answer. (i) 4x^2 - 3x + 7 (ii) y^2 + \sqrt{2} (iii) \sqrt{t} + \sqrt{2} (iv) \frac{y + 2}{y} (v) x^{10} + y^3 + t^6