A function f is said to be continuous at x=c when which of the following sets of conditions are satisfied?
a) f(c) exists and x→climf(x) exists
b) f(c) exists, x→climf(x) exists, and x→climf(x)=f(c)
c) x→c−limf(x)=x→c+limf(x) and f(c) exists
d) f′(c) exists