So they could become a reliable source of demand for such cars, which carmakers feel they ought to make but are unsure if they can sell.

因此，他们可能成这类汽车的可靠需求来源，这正是汽车制造商认为他们应该做的，但不能确定他们是否可以销售电动汽车的一点。

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Experts are unsure as to how much, and what kind, of genetic changes would be required for the virus to become a global health threat. Nor do they know how long this process might take.

至于病毒变异为人间传播类型从而威胁人类健康，其基因到底需要改变多少和发生何种改变，有关专家还难以确定，也无从知晓这种变异到底需要多长时间。

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