It is in the fourth paragraph that the authors propose a trial to study if honeybees’ in-take of Pyrethrum producing plants helps the honeybees defend against mite infestations. In the experiment, the authors offer honey bee colonies both Pyrethrum producing plants and "a typical bee food source such as clover" to determine if these different diets affect the bees’ susceptibility to mite infestations. In this context only option B fits. So, B is the answer.