In the \( x y \)-plane, the graph of a linear cquation of the form \( y=m x+b \) and the graph of an exponential equation of the form \( y=a b^{x} \) both contain points \( (5,-6) \) and \( (6,-8) \). If the point \( (r, s) \) is on the graph of the lincar equation and the point \( (r, t) \) is on the graph of the exponential equation, where \( 3<r<7 \), and \( s<t \), which of the following must be true?
A) \( 3<r<4 \)
B) \( 4<r<5 \)
C) \( 5<r<6 \)
D) \( 6<r<7 \)
