Which of the following expressions are polynomials in one variable and which are not? State reasons for your answer: $3 \sqrt{t} + t \sqrt{2}$

(D) The given expression is $3 \sqrt{t} + t \sqrt{2}$.
This can be rewritten as $3 t^{1/2} + \sqrt{2} \cdot t$.
$A$ polynomial in one variable is an algebraic expression where the exponent of the variable must be a non-negative integer (a whole number).
In the term $3 t^{1/2}$,the exponent of the variable $t$ is $\frac{1}{2}$,which is not a whole number.
Therefore,$3 \sqrt{t} + t \sqrt{2}$ is not a polynomial.