Which component of blood protects us from invading foreign material? plasma erythrocytes thrombocytes leukocytes

Correct D). Leukocytes

Leukocytes also called as white blood cells are the cells of the immune system that are responsible for protecting the body from the invading pathogen and infectious disease.

The monocytes of leukocytes absorb large particles, granulocytes secrete chemicals or toxin for the infectious agent and the lymphocytes attack and kill bacteria and viruses that cause infections.

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.