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【单选题】
根据某些条件对一个关系作水平分解，选择符合条件的元组组成一个新的关系，这样的操作系称为A.
投影
B.
选择
C.
连接
D.
自然连接
拍照语音搜题，微信中搜索"皮皮学"使用
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【简答题】用等效化简法分别求图6所示各电路中的电压U
【简答题】用等效变换求如图 (a) 所示电路中的电压 U 。
【简答题】求图示电路中的电压U。
【简答题】如图 所示电路中,硅稳压管 D Z1 的稳定电压为 8V , D Z2 的稳定电压为 6V ,正向压降均为 0.7V ,求各电路的输出电压 U 0 。
【单选题】She couldn’t decide whether to send him to hospital ________.
A.
or not to send
B.
or not
C.
or not to
D.
to or not
【简答题】求上图所示电路中的电流I和电压U。
【单选题】—What about _____ him a birthday card? —No, let's _____ him a computer . [ ]
A.
send, give
B.
sending, give
C.
send, giving
D.
sends, give
【单选题】________ a difficult situation, so you should send a message to him and give some advice to him .
A.
As he is in
B.
He is in
C.
Being in
D.
He being in
【简答题】It would be better for you (send)______ him an e-mail than to call him directly.
【单选题】________ a difficult situation, so you should send him a message and give him some advice.
A.
As he is in
B.
He is in
C.
Being in
D.
He being in
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