单位级别如何划分标准:一个英语问题。啊!又是英语!

来源:百度文库 编辑:神马品牌网 时间:2024/05/29 14:28:04
Why is a shape left between the rails of railway line where one piece joins the next?The space is left to let the rail expand when it gets hot.On a hot day ,the metal expands and if it (were not allowed)to do this ,the rail would bend .
请说明括号内的语法内容。书上说是虚拟语气,可是为什么是were而不是is

1.确实是虚拟语气
2.是和现在相反的虚拟语气,所以要用过去时
3.请注意,虚拟语气中be动词是不用was的,只用were

现在应该明白了吧!

是虚拟语气
虚拟语气的be动词只有were,没有was!

是虚拟语气