有一对夫妇，他们的基因型为Aa和Aa。第一胎生了一个基因型为Aa的孩子，如果再生一个基因型为AA的孩子的几率是（）

题干

A：1／4

B：1／3

C：3／4

D：1／6

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A

Lucy	I like sports. I have ten tennis balls, seven basketballs, four volleyballs and five soccer balls. I play tennis with my friends every day.
Mary	I have five baseballs, five volleyballs, two soccer balls. I like ping-pong. It's easy for me. I often play ping-pong with my classmates. I also have three ping-pong bats and lots of ping-pong balls.
Alice	I don't have any balls. I love sports, but I don't play them. I only watch them on TV.