To answer this question, you need to understand the meaning of the idiom "chew the fat."
Option A) Chat in an informal way about unimportant things - This option is correct. The idiom "chew the fat" means to have a casual and leisurely conversation about trivial or unimportant matters. It implies engaging in friendly and relaxed small talk or gossip.
Option B) Quarrel with each other - This option is incorrect. "Chew the fat" does not refer to quarreling or arguing with someone.
Option C) Do not care about diet - This option is incorrect. The idiom does not relate to dietary habits or concerns.
Option D) Cares a lot about diet - This option is incorrect. "Chew the fat" does not imply being concerned about one's diet.
The correct answer is A) Chat in an informal way about unimportant things.