GMAT Sentence Correction (SC) | Re: Not one of the potential investors is expected to make an

Here is the sentence using choice(C):

"Not one of the potential investors is expected to make an offer to buy First Interstate Bank until a merger agreement be signed by them with a provision for penalties if the deal were not to be concluded."

The pronoun "them" is ambiguous... who will sign the merger agreement? The bank itself is singular, so the only possible referent in this sentence
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