18. which of the following is a way for a reader to better understand why an author shares certain ideas within a primary source?

The answer is Understanding the author's use of structure and rhetoric.

D.Cather is critical of Chopin’s choice of themes.

Explanation:

Upon releasing her novel "The Awakening", in the end of 19th century, Kate Chopin was heavily criticized.

One of those critics was Willa Cather. She openly compared the protagonist of the novel, Edna, to Flaubert's Madame Bovary, in order to express unnecessary repetition of themes in Chopin's novel ("There was, indeed, no need that a second “Madame Bovary” should be written, but an author’s choice of themes is frequently as inexplicable as his choice of a wife").

However, besides criticizing choice of themes, Cather praises Chopin's writing style ("I shall not attempt to say why Miss Chopin has devoted so exquisite and sensitive, well-governed a style to so trite and sordid a theme").