Which of the following expressions are polynomials in one variable and which are not? State reasons for your answer: $x^{10} + y^{3} + t^{50}$

(D) The given expression is $x^{10} + y^{3} + t^{50}$.
$1$. $A$ polynomial in one variable is an algebraic expression where the exponent of the variable is a non-negative integer and there is only one variable present.
$2$. In the expression $x^{10} + y^{3} + t^{50}$,there are three distinct variables: $x$,$y$,and $t$.
$3$. Although the exponent of each variable $(10, 3, 50)$ is a whole number,the expression contains three variables.
$4$. Therefore,$x^{10} + y^{3} + t^{50}$ is a polynomial in three variables,not in one variable.