“When a ruler enjoys wealth and pleasure while all about him are grieving and groaning, he acts as a jailor rather than as a king.”
“Who quarrel more than beggars do?”
“Let him live on his own income without wronging others, and limit his expenses to his revenue.”
“It is less befitting the dignity of a king to reign over beggars than over rich and happy subjects.”
A. is the complex sentence. A complex sentence requires an independent clause that could stand alone as a complete sentence and a subordinate or dependent clause that could not stand on its own. "When" and "while" are both indicators of subordinate clauses called "subordinate conjunctions." The phrase "and limit his expenses to his revenue” is not a subordinate clause because it lacks a subject, and "than over rich and happy subjects” is not a subordinate clause because it lacks both a subject and a verb.