nce4-42课,第一段.An earthquake comes like a thief in the night,without warning.(as follows)An earthquake comes like a thief in the night,without warning.It was necessary,therefore,to invented instruments that neither slumbered nor slept.Some devi

nce4-42课,第一段.An earthquake comes like a thief in the night,without warning.(as follows)An earthquake comes like a thief in the night,without warning.It was necessary,therefore,to invented instruments that neither slumbered nor slept.Some devi
nce4-42课,第一段.An earthquake comes like a thief in the night,without warning.(as follows)
An earthquake comes like a thief in the night,without warning.It was necessary,therefore,to invented instruments that neither slumbered nor slept.Some devices were quite simple.One,for instance,consisted of rods of various lenghts and thicknesses which would stand up on end like ninepines.When a shock came,it shook the rigid table upon which these stood.If it were gentle,only the more unstable rods fell.If it were severe,they all fell.Thus the rods,by falling,by the direction in which they fell,recorded for the slumbering scientist the strength of a shock that was too weak to waken him,and the direction from which it came.
整段的时态求解释.

nce4-42课,第一段.An earthquake comes like a thief in the night,without warning.(as follows)An earthquake comes like a thief in the night,without warning.It was necessary,therefore,to invented instruments that neither slumbered nor slept.Some devi
An earthquake comes like a thief in the night,without warning.陈述句,一般时态.因为地震一直都是这样,是一般真理.
It was necessary,therefore,to invented instruments that neither slumbered nor slept.过去时态.因为早就应该发明地震仪了.
Some devices were quite simple.One,for instance,consisted of rods of various lenghts and thicknesses which would stand up on end like ninepines.When a shock came,it shook the rigid table upon which these stood.If it were gentle,only the more unstable rods fell.If it were severe,they all fell.Thus the rods,by falling,by the direction in which they fell,recorded for the slumbering scientist the strength of a shock that was too weak to waken him,and the direction from which it came.
过去时态.因为讲的是以前发明的地震仪的工作原理.