题干

下图表示环境条件发生变化后某个种群中A和a基因频率的变化情况,下列说法错误的是

A:环境条件发生变化后,使生物产生适应性的变异

B:P点时两曲线相交,此时A和a的基因频率均为50%

C:Q点表示环境发生了变化,A控制的性状更加适应环境

D:在自然选择的作用下,种群的基因频率会发生定向改变

上一题 下一题 0.0难度 选择题 更新时间:2018-12-26 07:14:04

答案(点此获取答案解析)

A

同类题3

下面文章中有五处需要添加小标题。请从以下选项(A、B、C、D、E和F)中选出符合各段意思的小标题。选项中有一项是多余选项。

A. Do some stretching.

B. Raise up your phone.

C. Buying a good phone.

D. Just put the phone down.

E. Take a load off.

F. Traveling by air?

Doctors say these tips will help people prevent trouble in the text neck.

____

Doctors encourage users to lift their phones to eye level rather than staring down at a screen. That way there's no added pressure from bending the neck downwards. Besides, users can look down at their phones with their eyes rather than bending their necks.

____

If the previous step is too awkward(笨拙的), simply don't use your smartphone as much. Many of the tasks performed on a smartphone can also be done on desktop-based apps.

____

For those who spend long periods of time on their phones, it's important to take breaks. Take a five-minute pause for every 15 minutes of smartphone use, and this one goes for tablet and laptops users too If you're sitting, get up, walk around and if possible, engage in step.

____

There are simple stretching exercises that can make muscles and tendons happy again after a long texting session. One is to turn the head as far as possible to the left, then back to neutral, and then all the way to the right. Next tilt(倾斜) the head ear-to-shoulder to one side, then return to upright, and then tilt to the other side.

____

Don't fall asleep. Often, travelers sleep in contorted(扭曲的) positions on airplanes and cars. When they do, the head often falls off the center of the neck, which can promote imbalance. Also, when in bed, it's important to avoid sleeping on the stomach.