Using the definition of continuity, which of the following functions are continuous?

A) f(x) = x2 + 1 for all x in R
B) g(x) = x3 - 2x2 + 3x - 1 for all x in R
C) h(x) = 1/x for all x in R
D) k(x) = sin(x) for all x in R