A long, difficult test. The quick, sneaky fox. That rich, delicious meal.
Explanation:
Read through the sentences and see which ones would still make sense if you added 'and' in between the two adjectives. The sentences I listed above are the ones that will still make sense with separation between the descriptions. With the two leftover sentences (Her deep green eyes. ; A brown leather couch.), it wouldn't make sense to split up the adjectives with and or a comma because it would either change the meaning of the sentence or sound wrong.
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