练习材料：
[Day 1751 2019-07-13]
Lesson 20-2 Snake poison
In fact, it would be an assistance to all carnivores though it would be a two-edged
weapon when they fought each other. But, of the vertebrates, unpredictable Nature
selected only snakes (and one lizard). One wonders also why Nature, with some snakes,
concocted poison of such extreme potency.
In the conversion of saliva into poison, one might suppose that a fixed process took
place. It did not; some snakes manufacture a poison different in every respect from that
of others, as different as arsenic is from strychnine, and having different effects. One
poison acts on the nerves, the other on the blood.
The makers of the nerve poison include the mambas and the cobras and their
venom is called neurotoxic.
任务配置：L0+L1+L4
知识笔记：
carnivores n. 食肉动物;
vertebrates n. 脊椎动物(包括所有哺乳动物、鸟类、鱼类、爬行动物和两栖动物);
concocted v. 调制，调合，配制(尤指食物或饮料); 虚构，杜撰，编造(故事、借口等);
potency n. 影响力; 支配力; 效力; (男子) 性能力，性机能;
arsenic n. 砷;
strychnine n. 士的宁; 马钱子碱;
mambas n. 树眼镜蛇(黑色或绿色，分布于非洲，有剧毒);
cobras n. 眼镜蛇(毒蛇，分布于亚洲和非洲);
venom n. (毒蛇、蜘蛛等分泌的) 毒液; 恶毒; 怨恨; 恶意; 歹心;
neurotoxic adj. 神经毒的；毒害神经的;
练习感悟：
