Hey guys!
This is a great question! It comes down to UNDERSTANDING the text at a deeper level than just the metalanguage - if you know the metalanguage and can contextually relate it, then you will do well. For example, advertisers often use elliptical sentence structures to ensure captivation of audience's attention. If you just said that ellipsis is used to create efficiency, therefore it achieves the persuasive purpose, you wouldn't score high. You need to look at WHY ellipsis is CAPTIVATING and ensures ENGAGEMENT in the advertising context.
Similarly, just say two strangers are having a chat on a train (they just met) and you notice a few pauses. If you just said that pauses allow the interlocutor to think, then you wouldn't score well. You need to look at the cultural context of pauses - silences are not tolerated with complete strangers, so pauses must be minimised with small talk (or phatic communication).
I hope this makes sense!