Lower pairs are kinematic pairs with（）
A. No contact
B. Point contact
C. Line contact
D. Surface contact
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The characteristics of Assur groups are（）
A. DOF=0
Basic link groups whose DOF=0 and cannot be further separated
C. Mechanical systems with lower pairs
D. Immobile mechanical systems with DOF=0
According to the types of contact, kinematic pairs can be classified into lower pairs and higher pairs. A higher pair refers to（）
A. Kinematic pair with point contact
B. Kinematic pair with line contact
C. Kinematic pair with surface contact
D. Kinematic pair with body contact
What are the main features of machines（）
Assembly of man-made components
B. Determinate relative motions among different components
Can conduct work/energy conversion
D. Well designed shapes and structures
What are the composition elements of mechanisms（）
A. Links
B. Kinematic pairs
C. Parts
D. Components
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