(a) Care
Lemmatisation reduces a word to its base dictionary form (lemma). The lemma of "caring" is "care", which is a meaningful root word.
Lemmatisation always produces a valid dictionary word, unlike stemming which may produce incomplete forms. "Car" is unrelated; "cared" and "cares" are inflected forms, not the base lemma. Examiners expect students to know that lemmatisation = meaningful root word (lemma).