6444. They knew by his sophomoric remarks that he was still knave in the field.

✅ The correct answer is option C.
Casual : relaxed and unconcerned.

Unpalatable : not pleasant to taste.

Immature : having or showing an emotional or intellectual development appropriate to someone younger.

Ignorant : lacking knowledge or awareness in general; uneducated or unsophisticated.

Sophomoric : pretentious or juvenile.

Synonym of Sophomoric is Immature