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"?
