问题
选择题
The girl had hardly rung the bell the door was opened suddenly, and her friend rushed out to greet her.
A．before
B．until
C．as
D．since
答案
答案：A
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The girl had hardly rung the bell the door was opened suddenly, and her friend rushed out to greet her.
A．before
B．until
C．as
D．since
答案：A
下表是某同学对自己吸入的气体和呼出的气体进行探究的结果（体积分数）
请你根据右表回答下列问题：
| 气体 | 吸入气体 | 呼出气体 |
| X | 78.25% | 74.88% |
| Y | 21.05% | 15.26% |
| CO2 | 0.04% | 3.68% |
| H2O | 0.66% | 6.18% |
（2）因参与新陈代谢而被人体消耗的是______．
（3）呼出气体中含有水蒸气．你的实验方法是______．
（4）X气体在呼吸过程中没有参与化学反应，但呼出气体中体积分数却减少了，原因是：______．