The skin of the poison dart frog contains deadly poisons called batrachotoxins. But the (i)_____ of the toxins has remained an enigma, as the frog does not (ii)_____ them. Now an analysis suggests that the melyrid beetle is the source. Collected beetle specimens all contained batrachotoxins, suggesting that these beetles are (iii)_____ by the frogs.
答案：B,E,G