Giải thích: Từ "which" trong dòng 13 đề cập đến

A. rào cản                   B. mô                          C. chất                         D. côn trùng

Dẫn chứng: If the physical barriers of the plant are breached, then preformed chemicals may inhibit or kill the intruder, and plant tissues contain a diverse array of toxic or potentially toxic substances, such as resins, tannins, glycosides, and alkaloids, many of which are highly effective deterrents to insects that feed on plants.

Chọn C