Which of the given signals are periodic?

• A. x(t) = 4 cos(5‚âà√¨‚àö√ët)
• B. x(t) = u(t) ‚Äö√Ñ√∂‚àö√ë‚àö¬® 1/2
• C. x(t) = 4u(t) + 2sin(3t)
• D. x[n] = 2sin(3n)