题干

医生为一对亲姐妹甲和乙进行染色体的DNA序列分析。若DNA序列没有发生任何变化,则结果应当是

A:甲的两条X染色体彼此相同,乙的两条X染色体彼此相同的概率为1

B:甲来自母亲的一条X染色体与乙来自母亲的一条X染色体相同的概率为1

C:甲来自父亲的一条X染色体与乙来自父亲的一条X染色体相同的概率为1

D:甲的任何一条X染色体与乙的任何一条X染色体都不相同的概率为1

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C

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    David Beckham was born in 1975 in London, at a place called Leytonstone. When he was a young boy, his greatest passion was in football. He played it whenever he had the chance. Sometimes he would go and watch a game with his friends. When David Beckham was 12 years old, he won the Bobby Charlton Soccer Skills award. This was an important step forward for this young boy, and it led him to go for a visit to a football training camp in Spain. As a boy he played for schools of Essex and also for his county team.

    In 1991, he became a trainee with Manchester United. This meant that he could practice football as much as he wanted to and play for the highly successful Manchester United Youth Cup team and Under-21 team. In April, 1995 he played his first football league game against Leeds Untied. During 1995 and 1996, David became a regular member of the team and Manchester United won in both football seasons, with David scoring many goals.

    His goals made him a household name. In the first game of the 1996-1997 season, he scored a surprising goal from beyond the halfway line; seeing the goalkeeper a little way out of his goal, Beckham became famous overnight. He continued to score astonishing goals, especially from free-kicks. The speed of one of his shots was timed at 157 kph. He also had the ability to make the ball go from left to right, or right to left, whenever he chose. Goalkeepers were never sure where the ball was going, and it regularly ended up in the goal.