A function is defined by mapping f : A B such that A contains m elements and B contains n elements and 1 n m then number of onto functions are ________

A function is defined by mapping f : A B such that A contains m elem

1.	A function is defined by mapping f : A B such that A contains m elements and B contains n elements and 1 n m then number of onto functions are ________
A.	<sub>r=1</sub> <sup>r=n</sup> <sup>n</sup>C<sub>r</sub> (-1)<sup>n-r</sup> r<sup>m</sup>
B.	<sub>r=1</sub> <sup>r=n</sup> <sup>n</sup>C<sub>r</sub> (-1)<sup>n-r</sup> r<sup>n</sup>
C.	<sub>r=1</sub> <sup>r=n</sup> <sup>n</sup>C<sub>r</sub> (-1)<sup>m-r</sup> r<sup>n</sup>
D.	None of the mentioned
Answer» B. <sub>r=1</sub> <sup>r=n</sup> <sup>n</sup>C<sub>r</sub> (-1)<sup>n-r</sup> r<sup>n</sup>