What is made of a central star around which various other non-star objects orbit?
a) planetary system
b) a nebula
c) a galaxy
d) black hole

I think that the answer is B

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.

where is the scientific experiment?