Read the Following Argument and Then Answer Multiple Choice Items

Multiple Choice

Read the following argument and then answer multiple choice items.
There is every reason to believe that the concussion crisis in NFL football will get worse. The speed and size of professional athletes have made American football more dangerous. Offensive linemen now average nearly 315 pounds-65 more pounds than they did 30 years ago. They launch that weight from a three-point stance, headfirst, at opposing linemen of nearly the same size. The impact of two such massive players produces a concussion in the cranium when the brain bangs against the skull. Professor of Neurology at Boston University, Dr. Ann McKee, notes, "when helmets clash, the head decelerates instantly, yet the brain continues to lurch forward, like a driver who jams the brakes on. Even though the skull is protected by a helmet, the brain itself is still in motion and a concussion is often the result."
-The opening sentence, "there is every reason to believe that the concussion crisis in NFL football will get worse," functions a which part of this unit of argument?

A) claim
B) warrant
C) grounds
D) backing