Your are right, \(\pi /3\) and 2\(\pi /3\) are solutions.
Of course each of these solutions can be replaced by the same number +k2\(\pi\) (with k being an element of Z) since sin x=sin (x+k2\(\pi\)) with k being an element of Z.
Those are angle measures expressed in radians.
If you translate in degrees you basically have to know that \(\pi\) radian=180 degrees
so \(\pi /3\) radian=60 degrees and 2\(\pi /3\)=120 degrees. So this two could be values of theta (A and B).
On top of that \(\pi /3+2 \pi\) could also be a solution (x+k2\(\pi\) with k=1). This can be translated to 60+360=420 degrees which is solution D.
So C. 240 degrees is the only one that could not be a value of theta.
