Explanation:

- The word "kook" refers to someone who is eccentric or unconventional, often in an amusing way.

- Option 1: Peculiar - This means unusual or odd, which is similar to "kook," not an antonym.

- Option 2: Foolish - While "foolish" implies a lack of good sense, it's more of a synonym than an antonym.

- Option 3: Sane - This means having a sound mind, the opposite of eccentric, making it a good antonym for "kook."

- Option 4: Illiterate - Refers to inability to read or write, unrelated to the meaning of "kook."