Given two sets A and B. Which of the rules below define a function f : A -> B? Q A = B = Z, to each m from A we assign n from B such that mn = 1. O A = {all points in the plane} , B = {all circles in the plane}, to each a we assign a circle f(a) with radius 1 and center x. O A = {all countries} , B = {all cities}, to each country I we assign its capital f(a). We assume that each country has a unique capital. O A = [-1, 1], B = R, to each a from A we assign f (x) - y to be a number y from B satisfying x | + y| = 1. O A = {all English words}, B = NU {0}, to each win A we assign f(w), the number of vowels in w