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，中上层阶级家庭都用上了中央供暖。
2
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。
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.