An individual has utility function u(x,y). Consider now utility functions v(x,y) = 23 * u(x,y) and w(x,y) = -12 * u(x,y). Which of the following is true? a. Utility functions v and w also represent the preferences, same as utility u b. Utility functions v also represent the preferences, but w does not c. Utility functions w also represent the preferences, but v does not