both physical and mental labour are important in the development of Civilization express in 200 words​​

Social development theory attempts to explain qualitative changes in the structure and framework of society, that help the society to better realize aims and objectives. Development can be defined in a manner applicable to all societies at all historical periods as an upward ascending movement featuring greater levels of energy, efficiency, quality, productivity, complexity, comprehension, creativity, mastery, enjoyment and accomplishment.[1] Development is a process of social change, not merely a set of policies and programs instituted for some specific results. During the last five centuries this process has picked up in speed and intensity, and during the last five decades has witnessed a marked surge in acceleration.[2]

The basic mechanism driving social change is increasing awareness leading to better organization. When society senses new and better opportunities for progress it develops new forms of organization to exploit these new openings successfully. The new forms of organization are better able to harness the available social energies and skills and resources to use the opportunities to get the intended results.

Explanation:

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation: