One of the ACT’s preferred tricks is to give you a sentence that looks like the following:
Mark Twain’s novel Huckleberry Finn is one of the most controversial, yet beloved books in all of American literature.
A. NO CHANGE
B. controversial; yet beloved
C. controversial, yet beloved,
D. controversial yet beloved
Because controversial and beloved are both adjectives, you do not need a comma between them. The answer is therefore D.
You can also think of the rule this way: comma + but/yet = period.
When you plug a period into the sentence, you get nonsense: Mark Twain’s novel Huckleberry Finn is one of the most controversial. Beloved books in all of American literature.
If a period doesn’t work, neither does “comma + but/yet.”