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菱形的两条对角线长分别是6cm和8cm，则它的面积是（　　）

A．6cm²

B．12 cm²

C．24 cm²

D．48 cm²

方程x²-6x+4=0的两个实根分别为x₁、x₂，那么（x₁-x₂）²的值为______．

补全对话。根据上下文的意思，把下列对话补充完整。

A: Hello, Nice to meet you!

B: 1._________________________! How long have you been in Zhuzhou?

A: For half a year.

B: 2._________________________?

A: It is a beautiful city.

B: Why did you come to study here?

A: Because my father got a job here.

B: Oh, 3.________________________?

A: He is a policeman.

B: Cool, I want to be a policeman, too. 4.________________________ ?

A: I want to be a singer.

B: 5.________________________?

A: Because I like singing very much.

电刺激神经干时向下传导引起的肌肉兴奋引发的电反应为（）

A.F波

B.H波

C.M波

D.P₁₀₀

E.N₇₅

生产经营单位安全生产管理人员安全培训包括典型事故和应急救援预案分析。