D
We have to prove Brad's reasoning that there could be some other explanation to be false .
Its not E because it is one of the other reasons hence strengthens his argument.
Jeneffer says the decrease in video rents rentals is due to the opening of Videorama store which not only rents but also sells videos cheaply(
First and only video store that rents and sells).
Brads argument covers just the rentals not the sale of videos. D strenthens Jennifers argument that opening of Videorama stores could have led to more people buying videos rather than renting videos from other stores.
Reduction in sales of other stores appox. = Sales in Rentals at Videorama (4000) + Sales of videos (From D)