Apure acid measuring x liters is added to 300 liters of a 20% acidic solution. the concentration of acid, f(x), in the new substance is equal to the liters of pure acid divided by the liters of the new substance, or f(x)=x+60/x+300. which statement describes the meaning of the horizontal asymptote?

a the greater the amount of acid added to the new substance, the more rapid the increase in acid concentration.
b the greater the amount of acid added to the new substance, the closer the acid concentration is to one-fifth.
c as more pure acid is added, the concentration of acid approaches 0.
d as more pure acid is added, the concentration of acid approaches 1.