Question

【题目】______the scientists have done lots of research on Mars, there is still much waiting to be discovered.

A.IfB.SinceC.UnlessD.Though

Answer 1

【答案】D

【解析】

句意：尽管科学家们在火星上做了大量的研究，但仍有许多有待发现的地方。

A. If 如果；B. Since自从，既然；C. Unless除非；D. Though尽管。根据下文there is still much waiting to be discovered.可知这里是though引导的让步状语从句。根据题意，故选D。