Which two statements are true?

An abstract class can implement one or more interfaces. It is not required to provide concrete implementations for all interface methods; any unimplemented methods remain abstract, and the class itself remains abstract.

Interfaces cannot extend classes (abstract or concrete). Interfaces extend other interfaces to form an inheritance hierarchy for interface contracts.

Interfaces can indeed extend other interfaces, allowing for the combination of method signatures from multiple interfaces into a single new interface.

An abstract class *implements* an interface; it does not *extend* it. Extension (`extends`) is used for class-to-class inheritance or interface-to-interface inheritance.

A concrete class can extend an abstract class. When a concrete class extends an abstract class, it is obligated to provide concrete implementations for all abstract methods inherited from its abstract superclass.

An abstract class can be extended by another abstract class. This allows for creating hierarchies of abstraction, where a subclass abstract class can further define or override abstract methods.