Scientists believe human cloning is just a matter of time but the assumption that human clones have already been born hasn't been proved yet.
科学家们相信人类的克隆只不过是时间问题，但是克隆人已经问世的说法还没有被证实。
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Scientists believe human cloning is just a matter of time but the assumption ________________ ____________ that human clones have already been born hasn't been proved yet.