The *heart* is the main organ of the circulatory system.
The circulatory system consists of three independent systems that work together: the heart (cardiovascular), lungs (pulmonary), and arteries, veins, coronary and portal vessels (systemic). The system is responsible for the flow of blood, nutrients, oxygen and other gases, and as well as hormones to and from cells.
Organisms that are well adapted to live together to in the same area over time.
The short sequences of characters that appear and can be
seen at the end of a filename preceded by a period is filename extensions. While
a sequence structure is a set of statements that execute in the order they
appear.
