he Umbrella Corporation是主语 had become是系动词
the largest commercial entity是表语 in the United States是定语
系动词加表语=谓语The Umbrella corporation had became 中的had 是什么成分啊？had become是系动词 become的过去完成时 had是助动词 become是过去分词 合在一起 是过去完成时 的谓语动词形式