Sentence Correction

I received a PM asking me to reply on the specific issue of pronouns in the above sentence and the broader issue of why pronouns sometimes seem to be ambiguous but the official answer says they're okay or vice versa.

Before I respond, I have a question: who wrote this problem? If it is a released question from the official test writers or if it is from a reputable company that has studied the test extensively, then it is worth discussing any apparent ambiguities. If the problem is not from a good source, however, then don't spend time agonizing over any ambiguities, because you don't know whether the real test would do something similar or whether this just isn't a well-constructed problem.

I'm a little skeptical of this one based on the first word: "since." Official test questions typically prefer "because" in this setup, reserving "since" for expressions related to time. (Yes, in the real world, we often use "because" and "since" interchangeably, and OG explanations will even do this too. But the questions themselves show a decided preference for not using the word "since" when the meaning is "because"!)

Also, as a short explanation, we have to check both logical meaning and structural composition of the sentence. In a quick glance at the problem above, I notice that the subject of the opening clause is "savings banks" and the two "they" pronouns that follow also function as the subjects of their respective clauses. Each "they" pronoun, then, both logically and structurally refers to "savings banks." That is often sufficient to indicate a proper antecedent on official questions, even when there are other plural nouns in the sentence.