（1）单选题
Which of the following statements is correct?
A In a use case diagram, the actors cannot have relationship between each other.
B In a use case diagram, the sub-actor can inherit its super-actor's relationships with use cases.
C In a use case diagram, the more relationships between use cases the better.
D The relationship of "extension" and "generalization" are the same, they can take each other's place.
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未经允许不得转载！第五章 面向对象分析--5.2 用例图【含答案】 软件工程