密封常用的方法有（）、小室密封、按垛密封以及按货架、按件密封等
A.办公密封
B.简单密封
C.随意密封
D.整库密封
参考答案：D
In the following statements about graph operations，which one is NOT correct
A．Finding critical path is an operation on directed graph
B．Finding critical path is an operation on undirected graph
C．Spanning tree of a graph may not be unique
D．Minimum spanning tree of a graph may not be unique
A．Sharing bodily fluids with an AIDS patient.
B．Shaking hands with an AIDS patient.
C．Serving meals to an AIDS patient.
D．Staying very close to an AIDS patient.
