If f is continuous and ∫ from 1 to 3 f(x)dx = 8, which of the following statements is true?
a) f(x) = 8 for all x in [1,3]
b) f(x) = 4 for some x in [1,3]
c) f(x) = 16 for some x in [1,3]
d) f(x) = 8x for some x in [1,3]