题目内容：
Today the energy problem becomes critical. It ____ an immediate solution.
A calls on B calls for C calls up D calls at
参考答案：【答案仅供学习，请勿对照自行用药等】
选择题：Today the energy problem becomes critical. It ____ an immediate solution.A calls
- 题目分类：习题答案
- 题目类型：选择题
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