ten dollars谓语动词用单数还是复数?

这涉及到主谓一致的问题,表示金钱,时间.距离.价格或度量衡的复合名词作主语时,通常把这些名词看作一个整体,谓语一般用单数.(用复数也可,意思不变.)
Eight hours of sleep is enough.
Twenty years stands for a long period in one's life.
二十年在人的一生里意味着一个很长的时期.
Four weeks are often approximately regarded as one month.