问题
选择题
If we_________ sunlight_________ a dry leaf with a piece of glass, it may start burning.
A．work; out
B．carry; out
C．focus; on
D．concentrate; on
答案
答案：C
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。