Answer: A. Eliminate useless words and phrases, negative statements, and
unnecessary adverbs, and express one idea at a time.
Option A logically makes the most sense. The other options might take away words that are needed in your writing. Let us still look at all the options and see which one applies the most.
[✓] Eliminate useless words and phrases, negative statements, and unnecessary adverbs, and express one idea at a time.
This one is a good answer. Since the words and phrases would be useless, removing them would combat wordiness without taking the meaning in your writing away.
[✗] Eliminate all three-letter words from your writing.
Why? All, and, but, for, had, has, out, you, his, her, any, was, one, etc are all three-letter words that may be commonly used!
[✗] Eliminate all proper nouns and pronouns from your writing.
Again I ask, why? Proper nouns can be important in writing if you are talking about a specific person, a specific place, etc.
[✗] Eliminate words that end with s.
This one is slightly silly. Even in the option it has the word "words" which ends in an s.