Can nitrogen be used as a first aid reagent for critically ill patients?

A, nitrogen can be used to make nitrogen fertilizer, so it can be used to synthesize ammonia to make nitrogen fertilizer, so A is correct;

B, nitrogen does not burn or support combustion, so it can not be used as automobile fuel, so B is wrong;

C, nitrogen does not burn or support combustion, so it can not be used as a fuel, and it can not be used as a propellant in the launching of rockets, so C is wrong;

D, nitrogen can not be

D. Nitrogen can't be supplied for respiration, so it can't be used as a first aid gas for critically ill patients, so D is wrong.

Therefore: A.