At P_C/P_W≡〖a*〗_LC/〖a*〗_LW, we know that foreign are in different between producing cheese and wine. Thus here we again have a flat section of the supply curve.
Finally, for P_c/P_W>〖a*〗_LC/〖a*〗_LW, both home and foreign will specialize in cheese production. There will be no wine production. So that the relative supply of cheese will become infinite.
The relative demand curve RD does not require such exhaustive analysis. The downward slope of RD reflects substitution effects. As the relative price of cheese rises. Consumers will tend to purchase less cheese and more wine, so the relative demand for cheese falls.