Subject-verb agreement requires the verb to match the number (singular or plural) of the subject. In (C), team is a singular collective noun, correctly paired with the singular verb is, making it the correct sentence. In (A), each is a singular pronoun, so are is incorrect; it should be is ready. In (B), neither is singular, requiring is instead of are. In (D), group is a collective noun typically treated as singular when acting as a unit (e.g., submitting one report), so has submitted would be more appropriate than have. While collective nouns like group can take plural verbs in some contexts (e.g., when emphasizing individual members), the singular is standard here due to the unified action.
Thus, (C) is the only fully correct sentence.