请教语法题72

The number of undergraduate degrees in engineering awarded by colleges and universities in the United States more than doubled from 1978 to 1985.

请教一下，这道题正确选项是more than doubled可是我不太清楚如果这样的话这里的谓语动词是什么呢？我还是个菜鸟，请牛牛指教一下吧！

多谢！

从答案来看也是double可我不太明白如果double作谓语动词的话，前面加more than又是怎么回事呢？能给解释一下这个语法结构吗？