Pascal’s rule relates three consecutive binomial coefficients in two adjacent rows of Pascal’s triangle. Which of the following is Pascal’s rule?
(a) (kn)=(k−1n)+(kn−1)
(b) (kn)=(k−1n−1)+(kn−1)
(c) (kn)=(kn−1)+(k+1n−1)
(d) (kn)=(kn−1)−(k−1n−1)