When a sentence has more than one subject, it's called a subject.

the underlined phrase is an example of : understatment

the correct answer is a "it describes nora and mrs. linde's relationship". opcions b and d are not related to the content of the passage in any way. option c could be appropiate but it does not fully capture the effect of the dialogue, while option a is quite appropiate, since the dialogue not only exemplifies the relationship between the characters, but it also captures the effect in the excerpt. we get to know that mrs linde bosses around and already knows nora.