It is a vital part of the immune system and helps to fight off infections.

BBC: Sunshine vitamin 'may treat asthma'

Part of the reservations system calculates the weight of the airplane based off passenger, fuel and luggage data, which is necessary for the airplane to safely take off.

WSJ: Delays Hit 1,300 American Airlines Flights

Officials in South Dakota warned residents to prepare for the worst by staying home and keeping off roads as the system moved through the eastern part of the state.

NPR: Spring Storm Crawls Eastward; Dumps Snow, Rain

The cloned cells would be genetically identical to the patient's own, so they could replace part of an ailing brain or heart without touching off a full-scale attack from the patient's immune system.

FORBES: Cloning's High Cost

The storm system swatted down power lines and uprooted trees, flicked big rigs on their sides and yanked off part of the terminal roof at Oklahoma City's Will Rogers World Airport, where some 1, 500 area residents had taken shelter in a tunnel.

CNN: In El Reno, a tornado 'looking at us dead in the eye'

While credit ratings have become an integral part of the financial system, making their way to valuation formulas and even legislation regulating pension fund investments, agencies have been off the hook for massive blunders, including their substantial responsibility in the 2007-2008 global financial crisis.

FORBES: Dodd-Frank Failing On Volcker Rule, Derivatives, Credit Rating Agencies