题干

如图为苯丙氨酸部分代谢途径示意图.苯丙酮尿症是由于苯丙氨酸羟化酶基因突变所致.患者的苯丙氨酸羟化酶失活,苯丙氨酸转化为酪氨酸受阻,组织细胞中苯丙氨酸和苯丙酮酸蓄积,表现为智力低下、毛发与皮肤颜色较浅等症状.下列分析错误的是(  )

A:一个基因可能会影响多个性状表现

B:生物的一个性状只受一个基因的控制

C:基因可通过控制酶的合成控制代谢过程,进而控制性状

D:在婴幼儿时期限制对苯丙氨酸的摄入可缓解患者的病症

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答案(点此获取答案解析)

B

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    One afternoon last week, I saw three tearful children from my son's school being comforted by teachers. That morning, my 11-year-old had stomach pains, retching(干呕)into a bowl. Talking to other mothers later, I heard about other children with stomachache or difficulty sleeping the night before.

What caused so much pain? Sports day. Sports day might be necessary at a highly-competitive independent school, but not at a village primary school. For the children who can fly like the wind, sports day causes no problem. For those who are overweight or just not good at sport, it is a nightmare(噩梦). Even for those who enjoy running but fall halfway down the track in front of the entire school and their parents, it can prove a disaster.

    Why do we put our children through this annual suffering? Some may say competition is character building; or it's taking part, not winning, that's important; or that it is a tradition of school life. I just felt great pity for those children in tears or in pain.

    Team games at the end of sports day produced some close races, wild enthusiasm, lots of shouting—and were fun to watch. More importantly, the children who were not so fast or quick at passing the ball were hidden a little from everyone's eyes. Some of them also had the thrill of being on the winning side.

    I wish that sports day could be abandoned and replaced with some other less-competitive event. Perhaps an afternoon of team games, with a few races for those who want them, would be less stressful for the children and a lot more fun to watch.