十万个为什么·科学启蒙30篇（2）

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为什么切洋葱时会流泪？

When you cut an onion, cells break open and release enzymes that mix with sulfur compounds.
These reactions create a volatile gas called syn-propanethial-S-oxide.
The gas rises and dissolves in the moisture of your eyes to form mild sulfuric acid.
This irritates nerve endings, triggering tear glands to flush out the chemical.
Chilling onions before cutting slows down the enzyme activity and reduces gas release.
Using a sharp knife causes less cell damage and therefore fewer tears than a dull one.
Wearing goggles or cutting near a running fan helps carry the gas away from your face.
Some onion varieties naturally contain less sulfur, making them 'tear-free' by design.
Scientists have even bred low-lachrymatory onions using gene-editing techniques.
Though annoying, this defense mechanism evolved to deter insects and animals from eating the plant.

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

These reactions create a volatile gas called syn-propanethial-S-oxide. 这些反应生成一种名为顺-丙烷硫醛-S-氧化物的挥发性气体。
Scientists have even bred low-lachrymatory onions using gene-editing techniques. 科学家甚至利用基因编辑技术培育出了低催泪洋葱。
This irritates nerve endings, triggering tear glands to flush out the chemical. 这刺激神经末梢，促使泪腺分泌泪水冲走化学物质。

这篇中文题目最接近哪一句？为什么切洋葱时会流泪？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？切洋葱时，细胞破裂，释放出与含硫化合物反应的酶。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 Onions Make You Cry When You Cut Them? How to cook noodles A maths worksheet

These reactions create a volatile gas called syn-propanethial-S-oxide.

These reactions create a volatile gas called syn-propanethial-S-oxide.

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：These reactions create a volatile gas called syn-propanethial-S-oxide.