by 15 percent/ at 15 percent有什么区别

问题描述:

by 15 percent/ at 15 percent有什么区别

by 15 percent指的是 (上升或下降了)15%
at 15 percent指的是 (上升或下降到)15%
至于是上升还是下降,这要看上下文的语境了.