Say your stack of rocks has one small rock at the bottom and you're trying to balance a bigger rock on top of it.

假设你的一堆石头底部有一块小石头， 而你正试图平衡上面的一块更大的石头。

Scientists in the United States say they have solved the riddle of why a large number of precariously balanced rocks located near the San Andreas fault line in California have never been toppled by earthquakes. Johansson Web explains.

美国科学家称已经探明为何加州圣安德烈亚斯断层线附近岌岌可危的岩石从未因地震而倒塌，约翰逊·韦伯报道。