Government funding for the arts must be increased if we

B talks about the previous artists, whereas the conclusion is about current artists.
Further, B does not provide alternative sources of livelihood.
The plan is to increase funding; goal: for artists to make a living & develop to greatness.

Something inherent in the plan or in the operating environment will either strengthen or weaken the argument.
D does the job of weakening b.cos, at present, artists have other options to survive and
not rely on government for funding to attain same greatness as past artists.

Conclusion : If the government doesn't increase funding, then potentially great artists will be forced to abandon their art solely because they need to make a living.

A. Many artists don't have the financial means to support themselves and devote themselves to their art full-time. -Supports the conclusion. Eliminate.
B. Da Vinci, Picasso, and Van Gogh are all remembered as great artists despite not receiving any government funding.- Does it tell us anything about today's artists ? Nope . Eliminate.
C. Artists that are controversial should not be given any government funding.- Controversial ? Out of scope. Eliminate.
D. Today's artists typically find nongovernment sponsors who support them in the same way that patrons did with Da Vinci, Picasso, and Van Gogh. - Yes, to weaken the conclusion - if artists find non-government sponsors then there would be no reason for them to abandon their art . Attacks the conclusion.
E. If artists who abuse government funding could be more efficiently discovered, whatever funds are available would be put to better use- Out of scope. Discusses how the funds could be put to better use. Eliminate.

Answer

The argument is that in the absence of increased government funding, potentially great artists will be forced to abandon their careers as artists.

A) - if anything, A strengthens the argument by reiterating that many artists are in need of funding.

B) - Could be deceiving, but this option is basically covered in more detail in option D. This might weaken the argument - but not as much as it would with specificity as to how Da Vinci, Picasso, and Van Gogh were able to survive without government funding.

C) - this is a value judgement and has no bearing on whether or not these artists (controversial though they may be) would be forced to abandon their careers without government funding.

D) - provides an alternate source of funding. there is another type of funding (non-government funding) that bridges this gap. This answer is similar to B, in telling us that Da Vinci, Picasso, and Van Gogh were not dependent on government funding, but it goes further and explains how they were able to achieve this, and that the option available to them is similar to the option that many artists use today - a non-governmental source of funding. I choose answer D.

E) - this answer is tricky. It may be the case that it is possible to get more out of existing funding, therefore not needing to increase it (or at least not by as much), but nevertheless reaching more artists. But this introduces a new concept (mismanagement of funds), and we don't know how much mismanagement is occurring, or if the recovered funds would be enough to support other artists. In the end, it does not weaken the argument as much as option D does.

The passage in a nutshell is saying that the ONLY WAY TO SAVE THE NEXT GENERATION OF ARTISTS (of the caliber of picasso , etc) is to resort to Government funding of the arts (or an increase of the level of funding all ready being given to the arts). He goes on to argue that if the GOVERNMENT does not increase its funding then most of the great artists will leave their trade in order to make a living..

(A) This answer choice only reinforces what the author is arguing, and if we assume it to be correct we have justified why the artist is CORRECT in arguing FOR the increase in government spending - WRONG!

(B) The author refers to the great artists of the past not to draw a parallel between their mode of finance (of their work and their livelihood) and those of MODERN artists, but only to describe a CLASS OF ARTISTS, therefore because this answer choice refers to the FUNDING of the great artists of the past it is OUT OF SCOPE

(C) The passage speaks nothing of CONTROVERSY , therefore this answer choice is the EASIEST to eliminate
as it is OUT OF SCOPE..

(D) This is the correct answer choice because it: does not dispute the fact that artists of today need FINANCE (or generate money) in order to stay in the trade, but it attacks the conclusion that GOVERNMENT MONEY is the only source of that finance. The tradition of PATRONS supporting Great artists has not changed since the days of picasso et al...

(E) This answer choice introduces a new concept, that of MISMANAGEMENT of funds, which is not present in the passage. Although it does provide an alternative to the author's view that AN INCREASE in funding is requred, it introduces a variable of the degree of which cannot be verified based on the information at hand (either in the passage or in the Answer choice)...

Why D is Superior to E:

D Provides factual information when it says that modern artists typically find alternate sources of finance... So their is no doubt whether most do or do not (they certainly do)..

E on the other hand leaves a lot of scope.. For example: If we take the answer choice at face value and go ahead and assume that ARTISTS are ABUSING funds, and if that were to stop existing funds could be better used, we do not KNOW whether the money freed up would be sufficient to keep the ARTISTS in Business..

Suppose the increase required to keep the artists from switching their vocation would be 100,000 but the money saved from the stopping the abuse is only 50,000 then what? Surely the remaining sum of money will be better used BUT the artists will still leave because that money that they get would not be sufficient to keep them floating...Therefore an INCREASE MAY WELL BE REQUIRED.. Provided certain assumptions E may well weaken the argument, but WE CANNOT say for certain whether it DOES, as in the scenario i have posted E may even strengthen the author's conclusion ..Therefore E as it stands is not a viable answer choice. D on the other hand CLEARLY mentions SUPPORT and even goes on to say that the SUPPORT would be in a similar fashion as the SUPPORT that had kept other great artists IN THE BUSINESS.. Clearly we can see that D will surely weaken the argument, whereas E may or may not!

Hope it helps !!