Using a 1:10 dilution, draw a serial dilution scheme where the final dilutions on the two different spread plates are 10⁻⁴ and 10⁻⁵. If the CFU/ml within the original stock is unknown, what is the number of cells in the original stock?

a) 10⁸ CFU/ml
b) 10⁹ CFU/ml
c) 10¹⁰ CFU/ml
d) 10¹¹ CFU/ml