14. Britain almost more than any other country in the world must seriously face the problem of building upwards， (that is to say)， of accommodating a considerable proportion of its population in high blocks of flats.

　　结构：共有2个谓语动词，其中主句谓语动词为must face.主干为：Britain must face the problem. almost more than any other country in the world作为Britain的后置定语。(that is to say)是插入语，意为“也就是说”。 两个of介词短语都在修饰the problem.

　　翻译：英国几乎比世界上任何国家都更加需要严肃对待向高空建筑房屋的问题，也就是说，要在很高的公寓楼里面容纳下人口总数的一大部分的问题。