Final answer:
While the text does not explicitly answer why Sister Rita won't let Frank talk, the context implies her silence could be due to the belief that speaking would be pointless, reflecting a common literary theme of silence as communication.
Step-by-step explanation:
The reason Sister Rita won't let Frank talk is not directly stated in the provided text excerpts.
However, based on the context of the various excerpts, where characters refrain from speaking or are described as unable to communicate effectively, one could infer that the reason might align with option 2), where Frank talks too much, or option 3), where he is not allowed to talk.
In literature, characters are often silenced or choose silence as a form of communication, to avoid conflict, or because they feel their words would be futile in a given situation, as suggested by the excerpt related to 'Sister Sara'.
Sister Sara herself chose not to reply but smiled sweetly, which might imply her belief that any words would be fruitless.
This might be the case with Sister Rita and Frank, where she decides that silence is a more powerful response than engaging with whatever Frank is saying or doing.