他必须清楚这个巨大珊瑚形阴渠。
He must have been familiar with the enormous madrepore of the sewer.
但是，要这样走，就必须彻底清楚这个巨大珊瑚形阴渠的所有分岔和直管。
But in order to do this, he must have been thoroughly familiar with the enormous madrepore of the sewer in all its ramifications and in all its openings.
错。底部的阴子是三角形的。
Incorrect. The shadow at the bottom is in a triangular shape.
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