hundreds of…等作主語時的主謂一致（用單數還是復數）

hundreds of, thousands of, millions of, billions of, dozens of, scores of 等作主語時的主謂一致怎么樣處置？用單數還是復數？如：

1. Hundreds of thousands of people ______ at risk.

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

第1題一定選are，這沒問題；第2題呢？如何選？

第2題也選 are。即句子的謂語動詞與 gallons 維持一致，不與 water 維持一致。

Hundreds of thousands of people are at risk. 有幾十萬人正處于危險中。

Millions of gallons of water are kept back by the dam. 這個堤壩攔住了滔滔的洪水。

又如：

Hundreds of tons of rubbish were moved. 搬運了數百噸垃圾。

Thousands of acres of forest were on fire. 數千英畝森林失火了。

Thousands of tons of steel were shipped out from the docks. 數千噸的鋼鐵從碼頭運走了。