What is similar between elements in horizontal rows in the periodic table?

A horizontal row on the Periodic Table is called a Period; and in the same Period, electrons fill the SAME valence shell. ... Full valence shells, i.e. the element has 2 OR 10 electrons, are stable electronic structure

Explanation:

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.

thinking it would be d not too sure but i think it's right