Question

Twenty years have passed since his father died.（YEAR作时间单位）

Answer 1

1. Twenty years have passed since his father died.

强调的是动作 passed,就是说年代是一年一年过去的,而不是整体一股脑儿就过去了.啰嗦一些也可以解释为： Since his father died, one year has passed, then another has pasesed and finally the rest of the years have passed one by one. They are 20 years in all.

2. 100 years is too long.

此处的 100 years 是个不可分割的整数,表示的是一个概念,换句话说即“一百年这个概念是一个很长的时间”,因此要把它视作单数.