题目内容
气袋常用的材质有聚四氟乙烯、聚乙烯、聚氯乙烯和金属衬里气袋等，它适用于采集化学性质稳定、不与气袋起化学反应的低沸点气态污染物。采样前气袋应清洗干净，无残留气体干扰、不漏气。采样时用现场空气清洗气袋（ ）次后再正式采样，采样后迅速将进气口密封。
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富集采样法适用于气体中被测物质浓度很低，或所用方法的灵敏度不高的情况，它包括 （ ）
富集采样法都需要使用外接动力设备，对样品进行富集采集。
U103Directions: Combine each pair of sentences into one.
Directions: Complete the passage by using appropriate tense of the given word.Before I left the office at 5 o'clock, I 1)____________(lock) the office door. When I passed by the office an hour later, I 2) ___________ (see) the door open. I felt a bit surprised, so I 3) ____________ (stop) and went in to take a look. When I saw the mess in the office, I knew the office 4) ___________________ (break into). I 5) _____________ (call) the police immediately. By the time the police arrived, my boss and my colleagues 6) ________________ (come) back to the office. Tom said that the 200 dollars he 7) ______________ (lock) in his drawer 8) ______________ (go). Dylan's camera, which he 9) _____________ (buy), was also gone. My boss suffered the heaviest loss. A few computers in the office 10) ________________ (steal). The police searched the office, but were unable to find any clues.
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