问题
选择题
____ most of the earth's surface is covered by water, fresh water is very rare and precious. [ ]
A. As
B. Once
C. If
D. Although
答案
答案：D
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____ most of the earth's surface is covered by water, fresh water is very rare and precious. [ ]
A. As
B. Once
C. If
D. Although
答案：D