Which of the flowing signals is not a periodic signal?

• A. \(x\left[ n \right] = {\cos ^2}\frac{\pi }{8}n\)
• B. \(x\left[ n \right] = \cos \frac{\pi }{3}n + \sin \frac{\pi }{4}n\)
• C. \(x\left( t \right) = \cos t + sin\sqrt {2}t \)
• D. \(x\left( t \right) = \cos \left( {t + \frac{\pi }{4}} \right)\)