题目内容：
If we do not promote renewable energy, the Earth’s natural resources will be used up soon.Unless _________________
, the Earth’s natural resources will be used up soon.
参考答案：
选择题：If we do not promote renewable energy, the Earth’s
- 题目分类：国家开放大学-开放英语4
- 题目类型：选择题
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Unless _________________
, the Earth’s natural resources will be used up soon.