When doctors reports on a brain disorder called CTE (caused by head on collisions) was rejected by the NFL orginastion even though actuaries confirmed a 67% risk of all NFL players getting the disease. CTE caused a person to inflict damage on themselves gradually until eventually committing suicide (for sources, watch movie "Concussion", based on a true story)
Allows you state the main idea of a the document in the form of an argument which will support with evidence throughout the document
Chances are that NASA's own website would be the best. That's about as primary of a source as you would find, and would also be more up-to-date than A would be.
