@hardik.jadeja
let us analyze both the examples that you have provided above, (you can find the entire question here)
Dr. Sayre's lecture recounted several little-known episodes in the relations between nations that illustrates what is wrong with alliances and treaties that do not have popular support.
(A) relations between nations that illustrates
(B) relation of one nation with another that illustrates
(C) relations between nations that illustrate
(D) relation of one nation with another and illustrate
(E) relations of nations that illustrates
note the difference - it is not episode, it is episodes
Here the correct answer is C because, it is 'episodes' that 'illustrate' not the 'lecutre'
Also note that it is 'illustrate' not illustrates (like you mentioned in the example) forthe obvious reasons.
Though we have a propositional phrase here, it is not related to the 'episodes' - hence 'that' refer to the episodes
on the other hand one can argue that 'that' refer to the 'lecuture'
2. In good years, the patchwork of green fields that surround the San Joaquin Valley town bustles with farm workers, many of them in the area just for the season.
(A) surround the San Joaquin Valley town bustles with farm workers, many of them
(B) surrounds the San Joaquin Valley town bustles with farm workers, many of whom are
(C) surround the San Joaquin Valley town bustles with farm workers, many of who are
(D) surround the San Joaquin Valley town bustle with farm workers, many of which
(E) surrounds the San Joaquin Valley town bustles with farm workers, many are
The closest contenters are A and B
Here 'that' can refer to both 'patchwork' and 'green fields'. please see the explanation below,
"patchwork of green fields that surround" vs. "patchwork of green fields that surrounds"
Both are possible. They have very slightly different meanings, but both meanings make sense. In the first case "that" is plural and refers to "fields." In the second case "that" is singular and refers to "patchwork." In the first case the sentence says that the patchwork is made up of green fields and that the green fields surround the town. In the second case it is the patchwork that surrounds the town. What's the difference? Both make sense to me.
I can make a preference to B only by considering "many of them" vs. "many of whom are"
Even then i consider this question as an ambiguous one.
My understanding is that relative pronoun 'that' agree with the immediately preceding noun, but we can see lot of anomalies to this among OG questions. hence we should consider the logic and the overall meaning in selecting the answer choice with relative pronoun 'that'.
