become是非延续性动词，它的延续性动词是been，became是过去式，这里因为前面有了has，那么就是现在完成时了，现在完成时的构成是have(has)+过去分词，而become的过去式是became，过去分词是become。
become
释义：
vi. 成为;变得;变成
vt. 适合;相称
例句：
Nobody knew the book would become such a classic.
当时没人知道这本书会成为经典。
If you're looking to become a marathon runner, having long legs is a great asset.
如果你想成为一名马拉松选手，有两条长腿是笔财富。
Will Apple Pay become a dominant player in the market? only time will tell.
Apple Pay能成为市场的主导者吗?只有时间才有答案。
常用搭配：
become one 成为一体，结合
become a member 成为一名成员/会员
become of 使遭遇…;…降临于;发生…情况
been
释义：
v. 是，有(be的过去分词)
n. (Been) (美)贝恩(人名)
例句：
The walls had been whitewashed.
墙壁被粉刷成白色。
His king had been checkmated.
他的王棋已被将死。
Fighting has been ferocious.
战斗一直很激烈。
常用搭配：
have not been 没有
have been there 全都知道，直接了解，亲眼看到
have been to 曾经到过
