The idea that there should be a high-degree mobility from one class to another would be acceptable to
A. Socialists and Capitalists
B. Conservatives and Liberals
C. Traditionalists and Liberals
D. Capitalists and Traditionalists
This is really going to depend on how your particular text or teacher defines all of these ideologies. However, I would argue that the best answer to this is B.
Liberalism is clearly the ideology that is most positive about the idea of people moving from class to class. Liberals believe that people should be able to do and be whatever their abilities allow. Conservatives, on the other hand, are harder to pin down on this issue. An American conservative would certainly agree that people should be able to move from class to class as their abilities and efforts warrant. However, conservatism is also a "status quo" ideology and some people might argue that conservatives would want the class hierarchy to remain the same.
However, I would argue that B is the best of the choices given.