某10kV线路长10km，已知导线电阻为0.5Ω/km，导线电抗为0.35Ω/km，

若方程x²-5x+6=0和方程x²-x-2=0的所有解构成的集合为M，则M中元素的个数为[ ]

A．4

B．3

C．2

D．1

哪些病主要是金黄色葡萄球菌引起的（）。

A.疖

B.痈

C.切口感染

D.急性骨髓炎

E.急性蜂窝炎

Object-oriented analysis (OOA) is a semiformal specification technique for the object-oriented paradigm. Object-oriented analysis consists of three steps. The first step is (71) . It determines how the various results are computed by the product and presents this information in the form of a (72) . and associated scenarios. The second is (73) , which determines the classes and their attributes; Then determine the interrelationships and interaction among the classes. The last step is (74) , which determines the actions performed by or to each class or subclass and presents this information in the form of (75) .

A. collaboration diagramB. sequence diagram
C. use-case diagram D. activity diagram

下列不属于空气负离子的生物学作用是（）。

A、降低血压

B、刺激骨髓造血功能

C、抑制气管纤毛运动

D、改善肺的换气功能

E、调节中枢神经的兴奋和抑制

征辟制