A certain cosine function has an amplitude of 5. Which function rule could model this situation?

a) f(x)=5cos(x)+3f(x)=5cos(x)+3

b) f(x)=3cos(x)+5f(x)=3cos(x)+5

c) f(x)=cos(5x)+3f(x)=cos(5x)+3

d) f(x)=cos(3x)+5