This paper formalizes a product structure with related characteristics based on AND/ORtree, and shows that the employment of this formalization can achieve a more flexible BOM design.
Every minute or so I could hear a snap, a crack and a crash as another tree went down.
几乎每隔一分钟,我就会听见又有一棵树倒下时发出的折断声、噼啪声和塌倒声。
《柯林斯英汉双解大词典》
3
When you think you are lost, sit down on a log, or a rock, or lean against a tree, and recite something that you have memorized, to bring your mind to a point where it's under control.