I think the following

The Argument says...

works of Richard Wagner are not used in the list of most frequently performed operas because Wagner's operas are notoriously expensive to perform on stage
but not the case of Wagner's popularity.


The argument will strengthen if we can show that the reason Wagner's operas are not included not because of his lack of popularity but because of expensive to perform on stage.So his popularity is super strong.

E says exact opposite (Apologies for my previous answer)

D wins

A list of the fifteen operas most frequently performed in recent times includes no works by the nineteenth- century German composer Richard Wagner. Although music producers tend to produce what audiences want, relative infrequency of performance probably does not indicate lack of popularity in Wagner's case, since Wagner's operas are notoriously expensive to perform on stage.

Which of the following, if true, most strongly supports the conclusion of the argument above？

(A)The list of most frequently performed operas does not include operas produced by small amateur groups. -This is irrelevant. We are worried about Wager and not "group"

(B)Some opera companies are backed by patrons who are willing to commit large sums of money in order to enjoy lavish productions. -We still don't know whether Wager's opera is supported or not. Irrelevant

(C)All of the fifteen most frequently performed operas of recent times are works that have been popular for at least 75 years. -Irrelevant

(D)More recordings have been produced recently of the works of Wagner than of the works of any other composer of opera. -Correct

(E)Operatic works of all kinds have been increasing in popularity in recent years. -This is close one. But option "D" is a better strengthener than this one. Out

Answer: D