In the suggest period between 200,000 and 12,000 years ago, humans were living a nomadic lifestyle. The humans of this period were hunter-gatherers, and they were constantly moving from one place to another in accordance to the food supply and climate conditions. Because of this constant movement and constant search for better hunting grounds and places where there's much bigger and more constant supply of fruits, vegetables, root plants, they managed to disperse in very big space and little by little to colonize the planet. In this period the cultivation of plants was still not taking place, and also the humans still hadn't managed to domesticate any wild animals, apart from the wolf which gave rise to the dog, but it was used for hunting, not as a food source.
Protective systems are methods of protecting workers from cave-ins of material that can fall or roll into an excavation, or from the collapse of nearby structures. As mentioned in earlier chapters, if an excavation is less than 5 feet deep, OSHA does not require a protective systems unless the competent person sees signs of a potential cave-in. (It is important to remember that a wall collapse in a trench four and 1/2 feet deep can still have serious results!) For trenches between 5 feet and 20 feet deep, shoring and sheeting, shielding, sloping and benching are all acceptable protective measures. It is up to the planners of the construction project and the competent person on site to determine which systems will work best. If an excavation is greater than 20 feet deep, a registered professional engineer must design the protective system.
Shoring systems are structures of timber, mechanical, or hydraulic systems that support the sides of an excavation and which are designed to prevent cave-ins.Sheeting is a type of shoring system that keeps the earth in position. It can be driven into the ground or work in conjunction with a shoring system. Driven sheeting is most frequently used for excavations open for long periods of time. Another type of sheeting, in which plates or shoring grade plywood (sometimes called Finland form) is used in conjunction with strutted systems such as hydraulic or timber shoring. These strutted systems are also referred to as active systems. The most frequently used strutted system involves aluminum hydraulic shoreswhich are lightweight, re-usable and installed and removed completely from above
Answer: Electron
Explanation:
Two type of microscopes that are used to view cells are optical and the electron microscopes.
The optical microscope, is also called the light microscope, and it uses visible light and lenses to magnify small objects and make them bigger. It is used in viewing cells as they appear big.
Electron microscope gives a high resolution images of specimens. The electron microscope is used in medicine to investigate tissues, cells, etc.
It means *prepare to fight*
