Which of these functions has a removable discontinuity at x=3x=3x=3?
f(x)=x−3x−3f(x) = \frac{x-3}{x-3}f(x)=x−3x−3
f(x)=x2−9x−3f(x) = \frac{x^2-9}{x-3}f(x)=x−3x2−9
f(x)=1x−3f(x) = \frac{1}{x-3}f(x)=x−31
f(x)=x+3x−3f(x) = \frac{x+3}{x-3}f(x)=x−3x+3