The right option is; b
It was a failed biological control mechanism for cane beetles is the best description of the cane toad’s introduction to Australia.
In 1935, cane toads were introduced to Australia from Hawaii as a biological control mechanism against the native grey-backed cane beetles that was destroying sugar cane crops. There was no adequate research about the history and ecology of the introduced control species as well as its interaction with the problem species. Therefore, the cane toads were not successful agents in reducing the native grey-backed cane beetles. Problems that occurred include; (i) the cane toads cannot climb and could not reach the beetles because the beetles usually feed on the upper part of sugar cane stalks, (ii) the two organisms are not seasonally compatible, (iii) the cane toads became invasive and feeds on many native animals (iv) the cane toads are poisonous throughout their stages of life and other organisms die when they eat them.