皮皮学，免费搜题
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搜题
【单选题】
钢液的二次氧化，将使钢中有害气体氮、氧含量（）。A.
增加
B.
降低
C.
保持不变
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参考答案：
参考解析：
知识点：
皮皮学刷刷变学霸
举一反三
【单选题】已知f 1 (t)=u(t),f 2 (t)=e -at u(t),可以求得f 1 (t)*f 2 (t)=():
A.
(1-e -at )u(t)
B.
e -at u(t)
C.
(1-e -at )u(t)
D.
e -at u(t)
【多选题】The Grand Canal was helpful in________.
A.
national unity
B.
economic development
C.
protecting the environment
D.
boosting the local agriculture
【简答题】已知f(t)=u(t)cos2t，其中u(t)为单位阶跃函数，试求f(t)的Fourier变换．
【单选题】The Grand Canal was first excavated in ________.
A.
the Han Dynasty
B.
the Warring States period
C.
the Spring and Autumn Period
D.
the Sui Dynasty
【单选题】Mass media was born. And this ________ a whole new world.
A.
open
B.
open up
C.
opened up
D.
opened
【简答题】听力原文：Q: In order to breathe, what did the mother put over their faces? In order to breathe, what did the mother put over their faces?
【单选题】已知f1(t)=2[u(t+1)-u(t-1)],f2(t)=u(t)-u(t-2),若f(t)=f1(t)*f2(t),则f(0)=( )。
A.
1
B.
2
C.
3
D.
4
【简答题】发动机的分类方法有:按进气系统是否增压分 和 。
【简答题】能源类型的分类,并举例。
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