Thanks for the question! (D) is wrong because we’re looking for something that weakens the argument. But if anything, (D) strengthens the argument! Because if the fines are ordinary business expenses, then they get to deduct those fines as taxes! And that means that the actual cost of the fines might be lower! So that’s why. Also, in general, the LSAT wouldn’t presume you to know that stuff about expenses. So since you don’t know, it’s just irrelevant.
Hope this helps! Feel free to ask any other questions that you might have.