Three million tons of coal was/were exported请问用单数还是复数

问题描述:

Three million tons of coal was/were exported
请问用单数还是复数

因为词组的中心词是tons。
所以应该选were。

was

复数
因为虽然coal不可数,但是前面的单位ton是可数的啦

主语是 tons, 复数, 用 were
of coal 是定语。