单项选择题

 由3 个结点可以构造出多少种不同的有向树？（    ）
A.
2 B.
3
C.
4
D.

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单项选择题
You need to attend an important meeting 10 minutes later, but your roommate want you to pick up his friend at the railway station, which of the following response is acceptable? ( ) A、I wish that I could help, but I have an important meeting to attend immediately. B、 That is impossible, I have no time. C、 You are kidding me? I Don’t you see I’m so busy today? D、There is no way, I have an urgent meeting soon.
单项选择题
赵女士，31岁，以发热待查入院，体温为39℃，持续五天，极度虚弱，病人清洁口腔的最佳方法
A．早晚刷牙
B．特殊口腔护理
C．进食后漱口
D．用生理盐水漱口
E．用棉签擦拭口腔
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