Which was the greatest factor in the world's population decline in the 1300s and 1400s? war disease infant mortality improved health care

There were four main factors in the world´s population decline in the 1300s and 1400s:

a. The climate: There was a drop of temperature that is referred to as the Little Ice Age. With freezing winters and cooler summers crops failed, which caused faming or mass starvation to occur.

b. Famine or starvation: The results of starvation were devastating. Tens of thousands of people simply starved to death. Epidemic illnesses carried off tens of thousand more whose resistance to disease had been weakened by hunger.

c. Spread of the Blac Plague or Black Death: In 1347 this new plague struck Europe and hit rich and poor alike. This was the plague in two forms, bubonic and pneumonic. Within a generation, plague killed off 40 percent of the English population and nearly 60 percent of the population in Northeastern France. The mass of death and the flight of population further undermined agriculture and added to the constant threat of famine.

d. The Hundred Years' war: The governments  of France and England added to this natural calamities by carring out a series of long, deadly wars, which are known as the Hundreds Years' war (1337-1453), and which agravated the problem of agricultural decline. The war took place entirely in France and contributed to the loss of lives and farmland.

The correct answer is "disease".

Explanation:

The worst epidemic disaster in history has been the Black Death, an infectious disease caused by the bacteria Yersinia pestis. This pandemic, known as well as the Great Plague or the Plague, caused the death of around 75 to 200 million people in Eurasia. As a result of the Black Death, from 1340 to 1400 the world's population declined by nearly of a quarter. It took nearly 200 years for the population number to rise again as how it was in 1340.

what are the options?