hundreds of…等作主语时的主谓一致（用单数还是复数）

hundreds of, thousands of, millions of, billions of, dozens of, scores of 等作主语时的主谓一致怎么样处置？用单数还是复数？如：

1. Hundreds of thousands of people ______ at risk.

2. Millions of gallons of water ______ kept back by the dam.

第1题一定选are，这没问题；第2题呢？如何选？

第2题也选 are。即句子的谓语动词与 gallons 维持一致，不与 water 维持一致。

Hundreds of thousands of people are at risk. 有几十万人正处于危险中。

Millions of gallons of water are kept back by the dam. 这个堤坝拦住了滔滔的洪水。

又如：

Hundreds of tons of rubbish were moved. 搬运了数百吨垃圾。

Thousands of acres of forest were on fire. 数千英亩森林失火了。

Thousands of tons of steel were shipped out from the docks. 数千吨的钢铁从码头运走了。