【分析解答题】Oil shales, (which may) furnish a (significantly) fraction of the world’s future energy, vary in richness, (yielding) from four to fifty percent oil (by weight).
【分析解答题】Oil shales, (which may) furnish a (significantly) fraction of the world’s future energy, vary in richness, (yielding) from four to fifty percent oil (by weight).
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