" However, if it absolutely must be one of the four examples, then "he" is immediately eliminated from consideration - you cannot use "he" with mankind ("they" seems within the realm of possibility, though). That leaves 1 or 3. If you're going to use "they," a plural pronoun, then the verb must be plural also.
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avid learnerI thought that you use "it" only when you are referring to a non human noun, such as an animal or a thing."it" may be used for nouns that refer to groups of people (e.g. "society", "(political) party", "company", "committee", etc. etc.).