Which of the following conditions is sufficient to conclude that a function f attains every value between f(a) and f(b) on the interval [a,b]?
a) f is monotonic on [a,b].
b) f is continuous on [a,b].
c) f is differentiable on (a,b) but may be discontinuous at a or b.
d) f has only finitely many discontinuities on (a,b).