I could not find the unit that is missing in your question so I can't discuss it and I will give you information about allusion in the literature works so you can find it by yourself.
Allusion can be put in the literature work directly or explicitly by the writer. It is a figure of speech by which author can make many references towards people, situations, events, object and many other things that he is showing in his work.
Audience or writer are the ones who must connect those allusion and idea of it to for understanding the idea of it.
This is an example of an allusion:
He studies all the time, and he is a regular Einstein.
This is an allusion example of a historical figure.
Children will react as they will be astonished (surprise) that ship which only sail in water how can it be stuck in between 2 rocks as in sea there is no rocks
