The right option is; a. soil degradation
Soil degradation most plausibly accounts for the reduction in corn yield.
Soil degradation is an environmental problem in which the condition or quality of soil is reduced due to its improper use usually for agricultural or industrial purposes. Soil degradation can reduce the physical, chemical and biological quality of soil. Soil degradation results in loss of organic matter, soil contamination, fertility decline, and soil acidity or alkalinity which can greatly affect agricultural productivity.
On the medieval world-maps it was represented only the part of the world known as the 'old world', which is consisted of Europe, Asia and Africa. Before the big discoveries, people living in this continents had knowledge only of this part of the world, while South and North America, Australia and Antarctica where still unknown to them, thus they are missing in the world-maps of this period.
Cays- they are formed when ocean currents transport loose sediments across a surface of a reef to a despositional node
