I will go for E. In case of A, if the rentals are more than sales, then the rentals can be 4001 also. Then the decline is still not explained. But, if ppl who bought the vid.s lend them to frnds, then the 4000 vid.s can be viewed by more. However, the second explanation is also not robust enough to support the statement that the sales have gone down by 10K as we do not know the number of frnds they woukld have lent to. But, we can assume without loss of generality that the vid once with the person can be lent to more than 1 frnd!!!