What is the most effective method for the prevention of disease ?
Thank you.

Washing hands is still the single most-effective way to prevent infections if done before and after preparing food or eating, caring for a sick person or treating a cut or wound.

answer; i believe that the correct answer is (lung);

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.