一项由甲、乙等5个人参加的相互传球游戏，第一次由甲将球传出，每次传球时，传球者将球等可能地传给另外4人中的任何一人，经过n次传球后，球在甲手中的概率为P_n．请写出P_n的递推关系式，并求P_n.

单项选择题A: I’m going shopping.B: Do you mind if I come with youA: (). You can carry my bag for me.

A. Thank you
B. It’s my pleasure
C. By the way
D. No, of course not
E. Never mind

单项选择题该处选项为（）。

A．This tour is the chance of lifetime．
B．It goes all over North America and South America．
C．It looks like you’re dreaming about something．
D．You’ll have to quit school and your job at the store．
E．My agent wants me to go on a tour with Art’s Jazz Band．
F．Have you told anyone about this yet
G．It would be a great opportunity!

问答题

单项选择题A: Thank you for looking after the cat for me.B.().I love cats.

A. Thank you
B. It’s my pleasure
C. By the way
D. No, of course not
E. Never mind

单项选择题正三棱锥A—BCD的体积为（ ）．