The answer would be Chemical
Nick does not know what to make of gatsby staff reasoning behind their relationship
The phrase from this passage which demonstrates that the author is identifying a source of debate is C. "the controversy stems from..."
To stem from something means to originate from, so this would be the logical answer.
<u><em /></u>The <em /><u>cat</u> (likes) to eat dog food.
<u>I<em /></u><em /> (enjoy) <em />reading.
<u>She</u> does not (like) physics.
In the last example, 'does not' is an auxiliary verb, also known as a helping verb.