Unlike the Han dynasty and the Roman Empire, Gupta India did not fall in part because of population decreases due to epidemic disease. All of the other answer options describe conditions or events that contributed to the decline of Gupta India.

The Byzantine Empire evolved from the Eastern half of the Roman Empire. When Rome fell, Byzantium continued on for several centuries before falling. Dynastic Egypt, The Aztec Empire, and the Maurya Empire are not geographically accurate, while the Ottoman Empire came after the Byzantines.

The primary objectives of the late-classical Byzantine rulers Justinian and Theodora were to restore the territorial integrity of the old Roman Empire, while also reforming the empire from within. The conquest of Africa, conquest of Italy, construction of the Hagia Sofia, and establishment of the Justinian law code are some of the many accomplishments of the two rulers that reigned during the mid-6th century CE.

The Western Roman Empire completely fell to Germanic peoples in the 5th century CE. The Eastern Roman Empire was able to survive and maintain its hold on the eastern territories through the end of the 6th century. The 'Byzantine Empire' was a later Medieval term for the Eastern Roman Empire.

The unification of China under the Qin dynasty was largely one of military domination. The Qin legal code had very harsh punishments for even minor transgressions, flouting Confucian and local traditions, and they did not ingratiate themselves with local elites. Although successful in unifying many disparate warring states, the harshness of Qin rule, and the preponderance of military solutions to societal problems, led to rebellion and civil war. Within 15 years the Qin state had collapsed.

After the turbulent transition from republic to empire, and the installation of the Emperor, Augustus issued a series of reforms that brought peace to the newly expanded empire. These included a census, wide-spread employment, and a postal service. 

The fall of Rome is the result of many factors, however, Christianity had little to do with the fall. The Byzantine Empire remained staunchly Christian after the Western Empire fell, and Christianity gained popularity throughout Western Europe through the turbulent times and dark ages that followed the collapse of the Roman Empire 

Egypt was an Empire that lasted for thousands of years. In fact, Cleopatra, the last Pharaoh of Egypt, lived closer to our time than when the Pyramids were built.

Although Ancient Egypt was conquered by certain outside groups for centuries, as with the Hyksos invasion, Egypt was always able to reassert its independence eventually, and Egyptian culture maintained even throughout foreign invasions.

Although some specific pharaohs of Egypt ruled for only short amounts of time, decades or less, ancient Egypt itself was one of the longest lasting civilizations and empires in history.

In the 4th and 5th centuries, the Roman empire faced increasing unrest. Factionalism among the elites, as well as attacks from abroad, caused many wealthy Romans to bury their silver for safekeeping.

Though Germanic tribes were increasingly aggressive in their attacks on Roman garrisons, the Italian peninsula, and even Rome itself, they had little interested in burying the silver they worked so hard to procure.

Germanic tribes had no traditions of burying their dead enemies with their luxuries, rather they had every intention of keeping their enemies' luxuries as spoils of war.

Silver was never theorized to cause disease.

Roman religious worship never included the burial of silver; silver from that period was buried for rational reasons.

As Rome expanded around the Mediterranean and declared itself an empire, the amount of time the average citizen had to spend in the army increased dramatically.

Originally, Rome had a fighting season between the end of winter and the harvest, and Roman soldiers fought near to home. With the birth of the empire, Roman citizens could be away from home for years at a time, traveling around much of the known world.

Throughout thousands of years of history, from small kingdom, to emerging republic, to gigantic empire, Rome adopted many styles of fighting, from a Greek style phalanx to a more maneuverable maniple system.

Rome built a navy, but it was never as good at naval combat than fighting on land.

Rome granted citizenship to important families who allied with them, and periodically certain emperors would grant citizenship to whole groups and tribes, usually in hopes of filling the ranks of the Roman army.