If we_________ sunlight_________ a dry leaf with a piece of glass, it may start burning.A.work; outB.carry; outC.focus; onD.concentrate; on
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C解析短语辨析。Work out计算出，锻炼；carry out执行；focus…on…把…聚焦于…;concentrate…on…把…聚焦于…;结合句意可知C正确。句意：如果我们用意块镜子把阳光聚焦于一片干树叶，它很快就会开始燃烧。