You count 212 colonies after plating 0.1 ml of a 1 * 10⁻⁶ dilution. What is the concentration of cells in the original sample?

a. 212 CFU/ml
b. 2.12 * 10⁹ CFU/ml
c. 2.12 * 10⁸ CFU/ml
d. 2.12 * 10⁻⁹ CFU/ml