I am trying to wrap my head around the usage of 'that' in these two sentences. While I got the answers correctly when I tried to understand the meaning of the sentence, I am wondering if there is any grammar rule that I am missing out here.
A study found that many autistic children share a set of mutations that regulate/regulates genes known to influence communication among brain cells.
The department is taking a stand against an approach that stand/stands to make an indebted citizenry more dependent on federal.
In sentence 1, it seems that that refers to 'a set' In sentence 2, it seems that that refers to 'approach'. Why does it not refer to 'a stand'?
Is there any rule that I can follow for 'that' in this context? For example, I read somewhere that 'that' must modify the noun immediately preceding it, but in example 1, that rule does not work. Also, somewhere else, I read that 'that' does not modify prepositional phrase. This works for 1 (of mutations is ignored), however for 2 this fails since (against an approach) is a prepositional phrase.