In the past few years,traffic problems(become)___more and more serious.

问题描述:

In the past few years,traffic problems(become)___more and more serious.
为什么用have become,

答案:have become
In the past few years 表示“在过去的几年里”,通常与现在完成时连用,而现在完成时的结构是:have/has + 过去分词.become是过去分词吗?是的,become的过去式是became,过去分词是become。过去分词与动词原形同形。