The correct answer is C. immature.
A sophomoric remark is one that is made by someone who is immature or inexperienced. It is often characterized by a lack of knowledge or understanding, as well as a lack of tact or social
awareness. In the context of the question, the speaker is saying that they know that the person they are talking about is still immature because they have made sophomoric remarks.The other options are incorrect because they do not accurately describe the meaning of the word “sophomoric.” Casual remarks are not necessarily immature, and they can be made by people of all ages and levels of experience. Unpalatable remarks are unpleasant to hear, but they do not necessarily indicate immaturity. Ignorant remarks are made by people who lack knowledge or understanding, but they do not necessarily indicate immaturity.
In conclusion, the correct answer is C. immature.