When you explain change -- for example, economic growth; economic growth is about change -- when you explain change, you use other things that have changed to explain change, rather than using the constant to explain change.
当你解释改变-- 例如，经济增长； 经济增长是关于改变的-- 当你解释改变， 你用别的改变过的事情来解释改变， 而不是用一个不变的事情来解释改变。