The key idea here: Emily’s action (retiring) is interrupted by her observation of someone else’s action (turning to the papers). The sentence should clearly show the cause-and-effect relationship between these two actions. The only sentence that conveys this without any grammatical or logical errors is Option B. The phrase "was hastily retiring" indicates that Emily was already in the process of retiring, but it’s interrupted. The phrase "saw him turn" is a simple past tense verb, showing that the action of her seeing him happened after she had already started retiring. This matches the narrative flow perfectly.

Option A: The placement of "but" is awkward and disrupts the flow of the sentence. It makes it seem like "but" is connecting "Emily" and "saw," which is not the intended contrast.

Option C: This sentence reverses the intended meaning. It suggests that Emily stopped retiring before she saw him turn to the papers, which doesn’t make logical sense. The cause-and-effect relationship is lost.

Option D: This sentence is overly repetitive and awkwardly structured. The repeated use of "and" makes the sentence feel disjointed. Moreover, it suggests that Emily stopped and then went to retire again, which contradicts the original idea that her retiring was interrupted, and she stopped as a result.

Hence, Option B is the best choice.