A continuous real-valued signal $x(t)$ has finite positive energy and $x(t)=0, \forall \; t<0.$ From the list given below, select ALL the signals whose continuous-time Fourier transform is purely imaginary.
- $x(t)+x(-t)$
- $x(t)-x(-t)$
- $j(x(t)+x(-t))$
- $j(x(t)-x(-t))$
