The upper part of this combo photo taken in October of 1990 shows five-year-old Zhang Si (R) posing for a photo with her mother at home in Taiyuan, capital of north China's Shanxi Province. Her family lived in a 60-square-meter home allotted by her parents' work unit. Household cooking and heating depended on honeycomb briquettes. The lower part of the combo photo taken by Zhan Yan on Nov. 13, 2018 shows 33-year-old Zhang Si (L) posing for a photo with her five-year-old daughter Han Siyang at home in Taiyuan. Zhang lives in a 160-square-meter apartment with underfloor heating and gas stove for cooking. (Xinhua)