[单选题]在下列何种情况下，可认为火势已被控制住：

正确答案 ：D

以上都对。

[单选题]用二氧化碳灭火可降低空气中氧气的含量，当氧气含量低于______时，绝大多数燃烧会自然熄灭。

正确答案 ：C

12%

[单选题]Diesel engines driving alternators operating in parallel must maintain a set frequency regardless of load changes. The governor characteristic used to accomplish this is known as _______.

正确答案 ：C

compensation

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