零边际成本。
因为风是免费燃料，所以风能的边际成本几乎为零。
The marginal cost of producing wind power is almost nothing, since the fuel—wind—is free.
而软件，即指令电脑从事何种工作的编程，可以电子方式进行生产、配送和营销，因此，其边际成本趋于零。
Software — the programming that tells computers what to do — can be marketed, manufactured, and distributed electronically, giving it a marginal cost that is close to zero.
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