You could tell them that the food chain is basically something that shows the feeding relationship between different living things. The food chain represents a series of food and energy are transferred from one organism in an ecosystem to another.<span />
The employee is the one that has to do most of the adjusting with the different roles of responsibilities they have to complete in each task that is assign to them.
Important changes in the Middle East between the 13th and 15th centuries include the 13 Century end of the First Crusade and the capture/founding of Jerusalem. After that came the rise of the Mongol/Turkish/Ottoman Empire during the 14th Century. The Ottoman transcontinental Empire controlled much of North Africa, Western Asia, and Southeast Europe. This led to the creation of important transcontinental trade routes and a boom of economic trade between the continents.
Pushing the Mongols north and fighting them, and the rebuilding of Beijing caused the Chinese decision to abandon major expeditions.
