The character or symbol which Marilyn should use to mark the new supporting sentence is:
According to the given question, we are asked to state the character or symbol which Marilyn should use to mark the new supporting sentence from her note taking.
As a result of this, we can see that during note taking, there is the outlining method which is used to separate ideas and mark headings and then subheadings.
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With this in mind, we can see that after making use of the capital letter A to make her first point, and she wants to add a supporting sentence, then she would have to make use of a small letter a or a Roman numeral i
Read more about note taking here:
https://brainly.com/question/5526423