C#.NET — Which statement about interfaces is correct?

Introduction / Context:
This item checks fundamental truths about C# interfaces: multiple implementation, interface inheritance, and the kinds of members interfaces can declare.

Given Data / Assumptions:

• C# allows a class or struct to implement multiple interfaces.
• Interfaces can inherit from multiple interfaces.
• Interfaces can declare properties, methods, events, and indexers.

Concept / Approach:
Eliminate false claims: single-interface-only implementation is false; exclusivity of implementation to a single class is false; prohibition on multiple base interfaces is false; and “interfaces cannot be inherited” is false. The remaining positive fact is that properties are allowed inside interfaces.

Step-by-Step Solution:

Verification / Alternative check:
Write interface IX { int P { get; set; } } and interface IY : IX, IDisposable { }. Implement both in various classes; compilation succeeds.

Why Other Options Are Wrong:
They contradict the multiple-interface implementation/inheritance features of C#.

Common Pitfalls:
Confusing class single inheritance (only one base class) with interface multiple inheritance (many interfaces).

Final Answer:
Properties can be declared inside an interface.