A shopkeeper places before you 41 different toys out of which 20 toys are to be purchased. Suppose m = number of ways in which 20 toys can be purchased without any restriction and n = number of ways in which a particular toy is to be always included in each selection of 20 toys, then `(m - n)` can be expressed as
A. `(2^(10))/(20!)(1.3.5"….."39)`
B. `(2^(20)(1.3.5"….."19))/(10!)`
C. `underset(r=0)overset(19)(II)((4r+2)/((20-r)))`
D. `(21/1)(22/2)(23/3)"…."(40/20)`