Classify the following as linear,quadratic,and cubic polynomials:
$(i)$ $x^{2}+x$
$(ii)$ $x-x^{3}$
$(iii)$ $y+y^{2}+4$

(N/A) $(i)$ $x^{2}+x$
Since the degree of $x^{2}+x$ is $2$,it is a quadratic polynomial.
$(ii)$ $x-x^{3}$
Since the degree of $x-x^{3}$ is $3$,it is a cubic polynomial.
$(iii)$ $y+y^{2}+4$
Since the degree of $y+y^{2}+4$ is $2$,it is a quadratic polynomial.