What does the associative property apply?

• A. Parallel connection of two systems is equivalent to a single system only in case of a continuous system
• B. Series and parallel interconnection of two systems is equivalent to a single system only in case of discrete system
• C. Series interconnection of two systems is equivalent to a single system in case of both continuous and discrete system
• D. Series interconnection of two systems is equivalent to a single system only in case of discrete