Agree with D. (Both are sufficient.)
Nope. Second Statement does not define any relationship between n and k!! Be careful.. While evaluating the second statement, forget everything that you know from first statement.
"To dream anything that you want to dream, that is the beauty of the human mind. To do anything that you want to do, that is the strength of the human will. To trust yourself, to test your limits, that is the courage to succeed."
- Bernard Edmonds