C is backwards. The newspaper subscriber argued that Arnot's conclusion is flat-out false because there is a gap in his support (the dubious assumption). C flips this. A "correct" version of C would be:

"She fails to consider that Arnot's conclusion may still be true even if some of the premises are nonetheless false."

Delete the junk between "colored paper" and "allows" and D makes a lot more sense.

Premise: "Colored Paper allows for a precise comparison of that color's impact in varying contexts."

+

D: "Observing the impacts of colors across varying contexts helps students to learn about the use of color."

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"When teaching art students about the use of color, teachers should use colored paper rather than paint in their demonstrations."