Sandstones

Sandstone is an arenaceous sedimentary rock composed mostly of feldspar and quartz and varies in colour (in a similar way to sand), through grey, yellow, red, and white. Since sandstones often form extremely visible cliffs and other rock formations, certain colors of sandstone may be strongly identified with certain regions. For instance, much of the North American West is familiar for its red sandstones.

Tumor

Tumor or tumour is an irregular growth or mass of tissue. A tumor can be either malignant or benign. Almost all tumors are examples of neoplasia, although certain developmental malformations or inflammatory masses may occasionally be referred to as tumors.

Neoplastic tumors are caused by mutations in DNA of cells, which interfere with a cell's capability to regulate and limit cell division. An accumulation of mutations is needed for a tumor to emerge. Mutations that activate oncogenes or repress tumor suppressor genes can eventually lead to tumors. Cells have mechanisms that repair DNA and other mechanisms that cause the cell to destroy itself by apoptosis if DNA damage gets too severe. Mutations that repress the genes for these mechanisms can also ultimately guide to cancer. A mutation in one oncogene or one tumor repressor gene is usually not enough for a tumor to occur. A combination of a number of mutations is essential.

China wall

The Great Wall is the world's longest human-made arrangement, stretching over about 6,400 km (4,000 miles) from Shanhai Pass in the east to Lop Nur in the west, along an arc that roughly delineates the southern edge of Inner Mongolia. It is also the biggest human-made structure ever built in terms of surface area and mass. A number of walls, referred to as the Great Wall of China, were built since the 5th century BC, the most famous being the one built between 220 BC and 200 BC by the first Emperor of China, Qin Shi Huang. That wall was much farther north than the current wall, built through the Ming Dynasty, and little of it remains.

Web portal

A Web portal is a site that functions as a point of admittance to information on the World Wide Web. Portals present information from diverse sources in a united way. Popular portals are MSN, Yahoo, and AOL. Aside from the search engine standard, web portals offer other services such as news, stock prices, infotainment and various other features. Portals provide a way for enterprises to provide a steady look and feel with access control and procedures for multiple applications, which otherwise would have been different entities altogether.

MS-DOS

MS-DOS (MicroSoft Disk Operating System) is an operating system commercialized by Microsoft. It was the commonly used member of the DOS family of operating systems and was the dominant operating system for the PC compatible platform during the 1980s. It has gradually been replaced on consumer desktop computers by a variety of generations of the Windows operating system.

MS-DOS was initially released in 1981 and had eight major versions released before Microsoft stopped development in 2000. It was the key product in Microsoft's growth from a programming languages company to varied software development firm, providing the company with essential revenue and marketing resources.

Whale

The term whale is ambiguous: it can refer to all cetaceans, to just the larger ones, or only to members of particular families within the order Cetacea. The last definition is the one followed here. Whales are those cetaceans which are neither dolphins nor porpoises. This can lead to some confusion because Orcas ("Killer Whales") and Pilot whales have "whale" in their name, but they are dolphins for the purpose of classification.