opening and closing structure

• 开闭结构

opening and closing structure的用法和样例：

例句

1. The valve will open and close at regular intervals.
   阀门将按一定的时间间隔开闭。
2. Her lips would part and close over these significant teeth.
   她的嘴唇不时地开闭在这两排惹人注目的牙齿上。