Which of the following functions are uniformly continuous on $\mathbb{R}$? (A) $f(x) = x$; (B) $f(x) = x^{2}$; (C) $f(x) = (\sin x)^{2}$; (D) $f(x) = e^{-|x|}$.
Which of the following functions are uniformly continuous on $\mathbb{R}$?\\
(A) $f(x) = x$;\\
(B) $f(x) = x^{2}$;\\
(C) $f(x) = (\sin x)^{2}$;\\
(D) $f(x) = e^{-|x|}$.