Houses built before 1939 use about 50% more energy per square foot than those built after 2000, mainly due to the tiny cracks and gaps that expand over time and let in more outside air.
出自-2010年6月阅读原文
英语六级真题
In many countries immigrants have been filling such gaps in the labour force as have already emerged (and remember that the real shortage is still around ten years off).
出自-2010年12月阅读原文
柯林斯高阶英汉双解学习词典释义
N-COUNT
缝隙；缺口；豁口；裂口
A gap is a space between two things or a hole in the middle of something solid.