Central heating was present in every upper-middle-class home by the second half of the 19th century.
到19世纪下半叶，中央供暖系统已出现在每个中上层家庭里。
2
Children of educated and upper-middle-class parents turn out to be far more curious, even at early ages, than children of working class and lower class families.
受过教育的孩子以及中上层家庭的孩子甚至在很小的时候就比工人阶级和下层家庭的孩子更有好奇心。
3
Children of educated and upper-middle-class parents turn out to be far more curious, even at early ages, than children of working-class and lower-class families.