A) many years that B) for many years since
C) since many years ago when D) many years ago that
Translate the following English into Chinese. Automatic block system is that within automatic block district, each section is divided by color light passing signals into several consecutive subsection or block. The occupation of subsection by train is authorized by the permissive aspect of the color light passing signals. Automatic block system shortens the space interval between trains in the same direction and increases running capacity at sections. But on single track lines where trains running in both directions on the same track, the efficiency of automatic block system is not so evident.
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