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【单选题】
现代数控机床的数控系统是由机床控制程序、数控装置、可编程序控制器、主轴控制系统及进给控制系统等组成，其核心部分是（）。A.
进给控制系统
B.
可编程序控制器
C.
数控装置
D.
主轴控制系统
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【简答题】若直线l的方向向量为（4，2，m），平面α的法向量为（2，1，-1），且l⊥α，则m=______．
【单选题】What is the major difference between B2B and B2C e-commerce?
A.
Customers interact freely in a B2B marketplace; they do not in a B2C marketplace.
B.
Consumers are fickle in a B2B marketplace; long time relationships are established between the consumer and its business partner in B2C e-commerce.
C.
Interaction between consumers and businesses are direct in the B2B market; they are indirect in the B2C market.
D.
The B2B marketplace does not involve consumers, just business partners; the B2C marketplace involves consumers.
【单选题】What is the difference between velocity and speed?
A.
There is no difference.
B.
Velocity is a vector, and speed is a scalar.
C.
Speed is a vector, and velocity is a scalar.
D.
Speed states only a magnitude, and velocity states a magnitude and direction.
E.
Velocity states only a magnitude, and speed states a magnitude and direction.
【简答题】已知l ∥ α，且l的方向向量为（2，-8，1），平面α的法向量为（1，y，2），则y=______．
【单选题】What is the difference between velocity and speed?
A.
There is no difference, they are both vectors.
B.
Speed is a scalar and velocity is a vector.
C.
Speed is a vector and velocity is a scalar.
D.
There is no difference, they are both scalars.
【简答题】已知l∥α,且l的方向向量为u=(2,m,1),平面α的法向量为v=(1, ,2),则m=____.
【简答题】若l的方向向量为（2，1，m），平面α的法向量为（1， 1 2 ，2），且l⊥α，则m=______．
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