Blank(i) - keywords to look out for "since it added considerably to the price of paint" & the reversal "but".
indicating though not readily accepted at the start, but once it caught momentum. So we are looking for a word which can somewhat mean "not readily".

"slow to be" fits this description

Blank (ii) - there is ample evidence which suggest that Impressionist wanted to just get out their houses and get inspiration from the world.
So we are looking for a word to mean "make or aid" this escape. "abet" is the only one which makes sense

Blank (iii) - interesting one. What Impressionists was unprecedented, so there was a lot of criticism which led me to think a possible to think a possible guess would be authentic.
Lets look at the options:
"finished" - somewhat related to the guess, moreover words preceding the blank back it
"magnificent" - a general trap option type, if you plug in the options, it may seem to fit, but note the general context, we also need words/keywords to back it - which is not the case here
"improvised" - doesnt fit

Hello from the GRE Prep Club VerbalBot!

Thanks to another GRE Prep Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.