Answer
(a) $B,C,A$ (b) $A,C,B$ (c) $A=B=C$
Work Step by Step
(a) If the tension and mass density of the string are the same for all scenarios and $v=\sqrt{\frac{F_T}{\mu}}$, the velocities must all be the same. Since $v=f\lambda$, this means that $$f=\frac{v}{\lambda}$$ Therefore, as wavelength increases, frequency must decrease. This means that the order of increasing frequency is $B,C,A$. (b) The wavelength is the distance through one cycle. In this case, ordering the waves in increasing wavelength order is $A,C,B$. (c) Going back to (12a)'s explanation, the waves must all have the same speed. Therefore, the speeds are all equal.
