十万个为什么·科学阅读30篇（4）

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为什么突然站起时眼前会冒金星？

Those quick flashes of light are called phosphenes, and they result from temporary drops in blood pressure.
When you stand suddenly, gravity pulls blood downward faster than your heart can pump it upward.
This causes brief under-perfusion of the retina—the light-sensitive layer at the back of your eye.
Without enough oxygen, retinal cells misfire, sending false signals that your brain interprets as light.
The effect usually lasts only a few seconds and disappears once circulation stabilizes.
Younger people experience it less often because their autonomic nervous system responds more quickly.
Dehydration, low iron, or standing after lying down for hours increases the chance of seeing phosphenes.
Unlike migraines or eye disease, this type of phosphene is harmless and requires no treatment.
Athletes sometimes use controlled versions of this effect during training to improve vascular responsiveness.
If dizziness or vision loss lasts longer than ten seconds, it’s wise to consult a healthcare provider.

听 → 读 → 学表达 → 懂 → 今天会说这一句 → 跟读录音 → 自己说一句。

The effect usually lasts only a few seconds and disappears once circulation stabilizes. 该现象通常仅持续几秒，待血液循环稳定后即消失。
Younger people experience it less often because their autonomic nervous system responds more quickly. 年轻人较少出现此现象，因其自主神经系统反应更快。
Athletes sometimes use controlled versions of this effect during training to improve vascular responsiveness. 运动员有时在训练中利用这种效应的可控版本来提升血管反应能力。

这篇中文题目最接近哪一句？为什么突然站起时眼前会冒金星？一次学校运动会的通知一份超市购物清单

课文第一句的意思更接近？那些短暂的闪光被称为光幻视，由血压暂时下降引起。今天学校放假了。请把窗户打开。

这一课主要在讲什么？（看英文标题） Why Do Some People See Stars When They Stand Up Too Fast? How to cook noodles A maths worksheet

The effect usually lasts only a few seconds and disappears once circulation stabilizes.

The effect usually lasts only a few seconds and disappears once circulation stabilizes.

第一版：录下来、回听、再听标准音。系统打分以后再加。

用今天的表达，自己说一句。

例子：The effect usually lasts only a few seconds and disappears once circulation stabilizes.