which is bad habit for use of laboratory refrigerator（）
A. Regular defrosting and cleaning
B. Disinfect the inner surface regularly
C. All chemicals stored shall be marked with the name , the date and the storer
D. The flammable solution placed in the ordinary refrigerator shall be noted on the door of refrigerator
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The instantaneous center of velocity of two links that form a higher pair is located__（）
A. On the common normal line of the contact point
B. On the common tangent line of the contact point
C. At the contact point of the two links
D. Infinity point along the common normal line of the contact point
The instantaneous center of velocity of two links that form a turning pair is located at（）
A. The center of the turning pair
B. On the circle of the turning pair
C. Any point on the circle of the turning pair
D. One of the two links
Lower pairs are kinematic pairs with（）
A. No contact
B. Point contact
C. Line contact
D. Surface contact
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
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