'GIRLS OF THAT CLASS'
Breakdown of the sentence into its key lexical, semantic and grammatical elements: 'Girls': The use of the concrete noun 'girl' in place of the proper noun 'Eva' suggests a sense of disrespect towards the working classes and a disregard of Eva's humanity. This lexical choice also posits Mrs. Birlings feeling of superiority over the working classes, due to the negative and juvenile connotations of the word 'girl' as opposed to 'woman'. 'That': Use of the demonstrative pronoun emphasises this lack of respect towards Eva, and a true sense of disgust towards her class - so much so that she cannot bring herself to use the correct name of the class. Minor sentence: The fact that this quote is a minor sentence emphasises the previous two points, in that it shows Mrs. Birling's lack of time and respect for the working class, as she doesn't even have time to use a high amount of words when talking about them. The quickness of the performance of this question underlines this, as it would highlight the upper class' disregard for the working class, and their view that they should be kept quiet and out-of-mind; this fact is truly highlighted here, as when Mrs. Birling speaks about Eva in this fast way the audience clearly understand how much the upper class wish to overlook and sweep past the lower classes.
We can use this analysis to understand Priestley's overall meaning and message to the play as a whole - this sentence is both a microcosm for the upper class overall and for the play's tensions between the representation of the Upper classes and lower classes.