Describe a situation in the book where someone risked his or her life to someone else

Risking a life for someone else is a heroic self-sacrifice, considering a situation in which a person place his own life in danger or even sacrificing it. An example of this is when an aircraft smashed into a frozen lake, six passengers were killed but others still alive. After 20 minutes, a helicopter arrived to rescue the survivors. A helicopter crew threw a life-ring to Arland Williams but he immediately gave it to the passenger next to him. When the helicopter back for third time, he did the same thing repeatedly. Then the helicopter come back the final time, but Arland was dead, he uses his last ounce of strength to save a complete stranger. 

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answer; limbic system;