Answer:
A
Explanation:
A coumpound sentence is putting 2 independent clauses together to form a sentence. The other ones don’t make sense and you should always put a comma in a compound sentence.
Augustus was the founder of the Roman Principate. The Roman elite was the highest class of the Principate, meaning they were of utmost importance.
The proper format is

No one really "said" it; it is the equation that represents Einstein's Theory of Relativity.
Answer: A controlled experiment is the only research method that can establish a cause and effect relationship.
Explanation:
The answer for this would be NURTURANCE OR HOSTILITY. Based on the Berkeley longitudinal studies, it is the nurturance or hostility that refers to the general stability that is present across time for the adult. This study of Berkeley covers the 50-year development of adults.