________muchisknownaboutthesurface

发布时间：2020-07-27 04:00:15

________ much is known about the surface of Mars, what happened during a long time remains unknown.A.ForB.WhileC.SinceD.Because

网友回答

B解析根据题意，此处应表示“虽然”，只有B项while可表示此意。since意为“既然”。
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