Which of the following cannot be the Fourier series expansion

Which of the following cannot be the Fourier series expansion of a periodic signal?

1. x(t) = 2cos t + 3 cos 3t
2. x(t) = 2cos πt + 7 cos t
3. x(t) = cos t + 0.5
4. x(t) = 2cos 1.5πt + sin 3.5πt

x(t) = 2cos πt + 7 cost, does not satisfy the Dirichlet condition, therefore, it can't be expanded as Fourier series.