The cause of the opening and closing is probably the difference in light.
开启和关闭的原因可能是光线的不同。
2
Opening up the door, in the light of the corridor, I found stunningly that fahter was standing in front of me!
打开寝室的门，借着楼道里暗暗的灯光，我不禁一惊，竟是父亲！
3
It's the difference between opening your refrigerator door and the light is just on, versus opening your front door to find a dark apartment and then fumbling for the light switch.