有一读者问：许多教科书和语法书上说，no sooner ...than结构中的 no sooner 之后应用过去完成时，实例如：
(1)No sooner had she finished reading the poem than students' questions began pouring in.
但我也在书上看到过不用过去完成时而用过去一般时或现在一般时，如：
(2)No sooner did they get to the school than it began to rain.
(3)No sooner am I half way through one reading list than I'm given another.
(4)No sooner was she back at home than she realized her mistake.
请问以上两种不同用法有何不同？
一般说来，no sooner...than 结构中的主句应用过去完成时，其 than 从句用过去一般时。但当主句的谓语动词所表的动作历时短暂时，即其与从句的谓语动词所表的动作之间的时隔很短时，亦可用过去一般时（或现在一般时），上述句（2）即是一例，再如：
(5)The name no sooner passed her lips than she turned away.
此外，当主句的谓语动词不强调动作的结果而强调状态时，亦可用一般时态。实例如上述句（3）和句（4），再如：
(6)It （the craft）was no sooner free from the incumbrance of the branches than it swung into the stream, sheering quite close to the western shore, by the force of the current.
