Question

If we_________ sunlight_________ a dry leaf with a piece of glass, it may start burning.

1. A.
   work; out
2. B.
   carry; out
3. C.
   focus; on
4. D.
   concentrate; on

Answer 1

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。