单项选择题

房间采用自然排烟时，其自然排烟口的设置选用以下哪种位置最好？( )

A.房间内墙的下侧部位
B.房间内墙的上侧部位
C.房间外墙的下侧部位
D.房间外墙的上侧部位
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单项选择题
Some villagers were going to celebrate an important wine festival（酒宴）in a few days' time, so they borrowed a huge barrel from the nearest town, put it in the village square; and decided that each of them should empty a bottle of the best wine he had into it, so that there should be plenty at the feast（宴会）.One of the villagers thought he would be very clever. If I pour a bottle of water in, instead of wine, no one will notice it, he said to himself, because there will be so much excellent wine in the barrel that the water will be lost in it. The night of the feast arrived. Everybody gathered in the village square with their bowls and their glasses for the wine. The tap（塞子）on the barrel was opened, but what came out was pure water. Everyone in the village had the same idea．One of the villagers poured a bottle of water into the barrel because ____.（ ）
A.hetriedtocheattheothers
B.theothersputwaterintoittoo
C.hethoughthewasclevererthantheothers
D.thewineinthebarrelwastoothick
单项选择题
某在建隧道用滤膜测尘法测定该隧道的粉尘浓度,采集了两个样品。样品-采样前滤膜质量W11=4000mg,采样后滤膜质量W12=4100mg；样品二采样前滤膜质量W21=5000mg,采样后滤膜质量W22=5120mg,流量计的读数Q=1.0m3 min,采样时间T=5min。结合上述内容,回答下列问题。（2）两个样品的粉尘浓度计算结果分别为（ ）。
A.20mg/m3;25mg/m3
B.25mg/m3;30mg/m3
C.25mg/m3;22mg/m3
D.20mg/m3;24mg/m3
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