If you don't know a person's last name, use 'ma'am' or 'sir'.
如果你不知道一人的姓, 你应称呼他为 'ma'am' 或 'sir' 。
This immense chasm has been formed by an underground stream which has tunneled a course through a flaw in the rocks.
这个深邃的洞穴是由一条地下暗泉冲刷岩石中的缝隙并使之慢慢变大而形成的。