Which of the following functions is continuous on the interval (−∞,∞)(-\infty, \infty)(−∞,∞)?
f(x)=x3+2x+1f(x) = x^3 + 2x + 1f(x)=x3+2x+1
f(x)=xf(x) = \sqrt{x}f(x)=x
f(x)=tanxf(x) = \tan xf(x)=tanx
f(x)=1x2+1f(x) = \frac{1}{x^2+1}f(x)=x2+11