A current is flowing north along a power line. The magnetic field above the wire must be directed towards :

 The direction of this magnetic field can be determined by the right-hand thumb rule. 

The right-hand thumb rule states that if we hold the current-carrying conductor in our right hand such that the thumb represents the direction of current flow; then the curled fingers around the conductor denote the direction of the magnetic field.
 

In this case, we should point the thumb along the north above the power line. We can see the curled fingers above the power line denote the magnetic field towards the east as shown in the figure.

Therefore, 'East' is the correct response.