Determine whether each of these functions is $O(x^2).$

a$)f(x)=17x+11$

b$)f(x)=x^2+1000$

c$)f(x)=xlogx$

d$)f(x)=\frac{x^4}{2}$

e$)f(x)=2^x$

f$)f(x)={|}_{{?}_{?}}{x}_{{?}_{?}}|*|$~$x$~$|$