A justifying principle must bridge the argument's premise to its conclusion: applied to the stated facts, it should yield exactly the conclusion drawn. The premise is that the scented-candle line has lost money for three consecutive years; the conclusion is that the line should be discontinued. The principle that makes that conclusion follow is a general rule that a product line losing money three years in a row should be discontinued, which is what E states. Applying E to the facts (a line that lost money for three straight years) directly delivers the owner's decision.
The other choices do not bridge the gap. A is out of scope: it concerns offering a wide variety of lines, not whether to discontinue an unprofitable one. B is an off-topic popularity claim that, if anything, argues for keeping the line, so it points the opposite way. C governs the converse case (lines that have been profitable, which it says to expand) so its condition never matches a money-losing line. D recommends tracking profitability but stops at gathering the data; it never tells the owner what to do once a line is found to be losing money. Only E supplies the general rule that, applied to the premise, justifies discontinuing the line, so the answer is E.