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【单选题】
下列物质中,哪个不是好氧堆肥过程产生的 。A.
二氧化碳
B.
水
C.
甲烷
D.
氨气
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反馈参考答案：
举一反三
【单选题】数字信号和模拟信号的特点是( )。
A.
模拟信号大小上、时间上均不连续，数字信号则相反
B.
数字信号大小上、时间上均不连续，模拟信号则相反
C.
数字信号、模拟信号大小上、时间上均不连续
D.
数字信号、模拟信号大小上、时间上均连续
【简答题】电子学研究的对象是载有信号的电信号,按其特点可以分为模拟信号和数字信号。模拟信号的特点是 ,数字信号的特点是 。
【简答题】We didn't know his telephone number, otherwise we _____ him. (A) would have telephoned (C) would telephone (B) must have telephoned (D) had telephoned
【单选题】We used to have a discussion, ___?
A.
did you
B.
didn’t we
C.
used we
D.
didn't used we
【单选题】--Why didn't you answer the phone this afternoon?--We didn't hear it. I was in the garden and Mum ______ a shower.
A.
has had
B.
had
C.
was having
D.
had been having
【单选题】— You didn't wait for Tom yesterday. — Yes, but we ______. He didn't come. [ ]
A.
needn't have
B.
didn't need to
C.
could have
D.
should have
【简答题】We didn’t go fishing because it rained heavily．（改为同义句） We didn’t go fishing________ ________ the heavy rain．
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