Thought process:
1. Since the transformers are ideal, power is constant throughout the circuit.
2. The load circuit tells us that P=VI=5*24=120W
3. Vp/Vs = Np/Ns ==> 240/Vs = 1000/500 = 2 ==> Vs=120V
4. P=VI, I=P/V=120/120=1.0A
So C.
LMK if i'm wrong, haven't looked at this content for a while...