练习材料：
Lesson20-2 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 onelizard). 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 asarsenicis 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.
应用配置：L0+L4
知识笔记： carnivores/ weapon/ vertebrates/ unpredictable/ lizard/ potency/ arsenic/ strychnine/ nerve/
练习感悟：用时46分。时间较赶，文字部分后面才补。
