问题
单项选择题
当矿井下含氧量减少至（）以下时，就可能发生窒息死亡事故。
A.20％
B.15％
C.12％
答案
参考答案：C
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当矿井下含氧量减少至（）以下时，就可能发生窒息死亡事故。
A.20％
B.15％
C.12％
参考答案：C
| 用方框中所给单词的适当形式填空，每词限用一次。 | |
2. Take the bus, and you will get to the university in five ______. 3. All of the children had a ______ school trip to the mountain. 4. I heard the ______ news that there was an accident on wall street this morning. 5. The river ______ again after the storm yesterday. |