For which of the following functions is f(r+b)=f(r)+f(b) for all positive numbers r and b?  Choose the correct choice from the following: A) a) f(x)=x^2 B) b) f(x)=x+1 C) c) f(x)=root x D) d) f(x)=2/x E) e) f(x)= -3x
f(r+b)=f(r)+f(b) Its e) f(x)= -3x
<result>E</result>
For which of the following functions is f(r+b)=f(r)+f(b) for all positive numbers r and b?