Official Explanation
On the basis of a loose sense of this sentence’s meaning, you might be tempted to select the first choice, amorphous. After all, this sentence basically tells you that you should wipe out hatred before it gets too dangerous. Clearly, if hatred is vague or amorphous, it is less formidable than if it is well-defined. However, this reading of the sentence is inadequate: it fails to take into account the sentence’s key phrase.
The key phrase here is “may grow to dangerous proportions.” The writer fears that class and race hatred may grow large enough to endanger society. He wants us to wipe out this hatred before it is fully grown. Examine each answer choice, eliminating those answers that carry no suggestion that something lacks its full growth or development. Does overt suggest that something isn’t fully grown? No, it suggests that something is obvious or evident. Does rudimentary suggest that something isn’t fully grown? Yes, it suggests that something is unfinished or immature. This may well be one of your two correct answer choices.
Look for a second word that suggests a lack of full growth. Does independent suggest that something isn’t fully grown? No, it suggests that something is free and unconstrained. Does threatening suggest that something isn’t fully grown? No, it suggests that something is a source of danger or cause for alarm. Only one word is left: embryonic (at an early, incomplete stage of development). If you substitute embryonic for rudimentary in the sentence, you will not change the sentence’s essential meaning. The correct answer choices are rudimentary and embryonic.
Answer: C,F