Which is of the following statements is true about the Command Pattern? (Check all that are correct. More than one answer is possible)

A. It is the same as Chain of Responsibility pattern combined with Facade pattern.

B. The main Command Class must have a private Constructor.

C. It facilitates the undo operation.

D. It must always be used as a Singleton Pattern Class.

E. It calls the relevant function indirectly.

F. The Command Pattern can be used to keep a list of operations to be able to undo them when it is required.