Sneha2021
KarishmaB GMATNinjaWhy "but" cannot be a coordinating conjunction in C & D?
(D) who are under criminal investigation, but they
A federal....people under investigation(IC), but they (IC)
"They" must refer to federal acc to structure but it is plural so only single referent for "they" is people. Therefore I did not find it ambiguous. Please help me to reject C & D.
Thank you for your help

The issue is logic, not ambiguity.
Because we have an independent clause following "but" in (C) and (D), we'd expect a contrast between the first independent clause and the second.
This gives us the following construction:
Quote:
A federal advisory panel proposes expanding a national computerized file..., BUT they have not yet been charged.
The portions in red and blue don't seem to have any logical relation at all. Why would it be surprising that people haven't been charged in light of the fact that an advisory panel wants to expand some computer file?
However, in (E), we don't have an independent clause after the "but." Instead, we have the verb phrase, "have not yet been charged." This very phrase must be parallel to another verb phrase.
Take another look at the relevant portion:
Quote:
People who are under criminal investigation but have not yet been charged.
Now the portions in red and blue are two verb phrases that have a logical connection. Even though these people are under investigation, they haven't been charged. This makes way more sense.
So, you're right. (C) and (D) aren't wrong because they contain an ambiguous pronoun. They're wrong because they contain two parallel independent clauses that create a nonsensical meaning, and (E) fixes the problem by creating parallelism between two related verb phrases instead.
I hope that clears things up!