Which among the following are true about Robert K. Merton's theory of structural-functionalism?

A. A structure may be dysfunctional for the systems as a whole and yet may continue to exist.

B. All standardized social and cultural beliefs and practices are functional for society as a whole as well as for individuals in society.

C. Actions have both intended and unintendeded consequences.

D. All structures are not indispensable to the working of social systems.

Choose the correct answer from the options given below: