Not sure what your question is!

doesnt the answer A present a participle issue?

if you notice that that in the original correct section of the sentence teh word "APPROVED" is used and that remained is taking place before the approval. Thus, HAD must be used in order to have a past perfect. Correct me if I am wrong,

Thanks

I think you explained the ans in the easiest way possible. This way any answer of this type can be solved in seconds.

Khurram

OG question. I chose A

IMO A

IMO A
While reading the original sentence, it is clear that site of Battle of Princeton is one among the eight battlefields that had not been developed before June on 1989. Hence, past perfect tense (had remained) also makes sense.

Also, D changes meaning. In original sentence, 'only' modifies 'eight' (so, author wants to stress that there were only eight revolutionary battlefields), while D says: 'only one of eight...' ('only' modifies 'one').

(A) one of only eight Revolutionary War battlefields that had remained undeveloped

(B) one of eight of the only Revolutionary War battlefields that have remained undeveloped

Tense problem
(C) one of the only eight undeveloped Revolutionary War battlefields that remains
tense problem
(D) only one of eight Revolutionary War battlefields to remain undeveloped
wroing modifier
(E) only one of the eight remaining undeveloped Revolutionary War battlefields
wrong modifier[/spoiler][/quote]