LSAT-19-3-14

valarie

14.   Caffeine can kill or inhibit the growth of the larvae of several species of insects. One recent experiment showed that tobacco hornworm larvae die when they ingest a preparation that consists in part of finely powdered tea leaves which contain caffeine. This result is evidence for the hypothesis that the presence of non-negligible quantities of caffeine in various parts of many diverse species of plants is not accidental but evolved as a defense for those plants.

The argument assumes that

(A) caffeine-producing plants are an important raw material in the manufacture of commercial insecticides

(B) caffeine is stored in leaves and other parts of caffeine-producing plants in concentrations roughly equal to the caffeine concentration of the preparation fed to the tobacco hornworm larvae

(C) caffeine-producing plants grow wherever insect larvae pose a major threat to indigenous plants or once posed a major threat to the ancestors of those plants

(D) the tobacco plant is among the plant species that produce caffeine for their own defense（E）

(E) caffeine-producing plants or their ancestors have at some time been subject to being fed upon by creatures sensitive to caffeine

What the meaning of E? What's the meaing of " been subject to being fed upon"?

ztlbox

就是能产生咖啡因的植物和他们的祖先在某一时期内遭受到（subject to ）一些对咖啡因敏感的生物的侵害，这些生物把这些植物当食物（being fed upon ）

从而在结论is not accidental but evolved as a defense for those plants

和Caffeine can kill or inhibit the growth of the larvae of several species of insects.（大前提） One recent experiment showed that tobacco hornworm larvae die when they ingest a preparation that consists in part of finely powdered tea leaves which contain caffeine（小前提）架桥。