The closest antonyms are words that have opposite meanings.
In the given options:
- Option A: "essential" and "optional" are antonyms because "essential" means necessary or extremely important, while "optional" means not required or not necessary. Therefore, option A fits the criteria of closest antonyms.
- Option B: "innocently" and "obediently" do not represent antonyms. They do not have opposite meanings.
- Option C: "estimated" and "separated" do not represent antonyms. They do not have opposite meanings.
- Option D: "invasion" and "presence" do not represent antonyms. They do not have opposite meanings.
Therefore, the correct answer is option A: essential and optional.
