Zhongguancun Building #28 within the Zoology Institute 动物研究所 compound 宿舍. If I remembered it right, the configuration of the building: two entrances (二个门洞) and two apartments on either side of the stairs. Mom lived on the third floor to the left side of the stairs from right most entrance. She was assigned a room that was facing the court yard, and sandwiched between two rooms or one room on the left and right was the shared-kitchen, by the bathroom. The small bathroom was actually just a toilet at the end of the hall.