upgrade和improve区别

Upgrade是升级的意思，而 improve 是提高或者改善的意思。区别可以从以下例子看出：

Every time we go back to China, we can see and feel the difference, public transport has been upgraded, traffic is improved. 每次回到中国，都能看到和感受到不同，公共交通升级了，交通改善了。