A box contains 2 white and 2 black balls. A ball is drawn, replaced, and the box is shaken before drawing a second ball. Let A be the event "the first ball drawn is white" and B be the event "the second ball drawn is black". Which of the following statements is correct?
a) P(B∣A)=21,so A and B are independent
b) P(B∣A)=32,so A and B are dependent
c) P(B∣A)=41,so A and B are independent
d) P(B∣A)=21,so A and B are dependent