20. Carbohydrates are usually composed of sequences of carbon (C), hydrogen (H), and oxygen (O). How do proteins differ from carbohydrates?
A All proteins contain iron (Fe).
B. All proteins contain helium (He).
All proteins contain nitrogen (N).
D.
All proteins contain potassium (K).

Structurally, proteins are different from carbohydrates because all proteins contain nitrogen (option C).

Explanation:

The basis of the chemical composition of proteins is carbon, hydrogen, oxygen and nitrogen, so all proteins have nitrogen in their structure. Some proteins also possess phosphorus and sulfur atoms, among others.

Proteins are biomolecules formed by the union of multiple amino acids through carboxyl-amino bonds, called petidic bonds. Their content of nitrogen and other atoms in their structure is what makes them different from carbohydrates.

The other options are not possible because:

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.