The idea that natural assets are substitutable makes some environmentalists (including some contributors to the report) nervous.

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At the extremes to an economist everything is substitutable.

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The FDA has yet to pass judgement on the subject of substitutable or interchangeable biosimilars, but consensus indicates that such a status could be conferred on a biosimilar if it is supported with more extensive clinical testing.

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It also implies that they are substitutable.

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