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【单选题】
瓦斯浓度是指瓦斯在空气中按（ ）计算的比率，以％表示。A.
体积
B.
重量
C.
密度
D.
质量
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【单选题】听力原文：M: Hello, everyone. We're talking about Stella Hampton, famous Hollywood actress. Before the break, we were talking about your life, Stella, before you became a big star. W: Yes... Oh, but do we ...
A.
When she was working in a department store.
B.
When she was working for a painting house.
C.
When she was working in a taxi company.
D.
When she was working as an actress in Hollywood.