What were your problems ten years ago__ become mine.是填have还是 has?请高手告知.Thousanda of thanks

题目

What were your problems ten years ago__ become mine.是填have还是 has?请高手告知.Thousanda of thanks
尤其是最后一个答案较为详细.根据what所指的含义来确定谓语动词的数：What he needs ___ money.填is.而What he needs ___ some books.要用are.我的问题中的what所指的是your problems,填has似乎讲不通.劳驾您再次费心给我举几个例子吗,以便使我透彻的明了?

答案

has.
因为可以这样认为:
ten years ago 是修饰 your problems 的,所以对句子成分没有影响,可以不去看它.所以句子简化成:
what were your problems __ become mine.
又 were your problems 是修饰 what 的,所以对句子成分没有影响,拿掉后句子依然成立.所以句子再次简化成:
what __ become mine.
现在很清楚了,应该填 has 了.