Which illustration indicates a coordinated turn?

A coordinated turn is characterized by a specific bank angle that allows the aircraft to maintain a balance between lift and centrifugal force, resulting in a smooth and stable change in direction. When an aircraft is in a coordinated turn, it is essential that the bank angle is not too steep or too shallow, as this could lead to either a loss of altitude or an increase in speed due to unbalanced forces.

In the context of the provided choices, the illustration that shows a turn with a bank angle clearly demonstrates what a coordinated turn looks like. This representation typically shows the aircraft banking into the turn while maintaining an appropriate angle, ensuring that the forces acting on the aircraft are balanced. Unlike other options that represent level flight or climbing, which do not involve directional changes through banking, the depiction of a turn with a bank angle highlights the essential aerodynamic principle of coordination in turns, thus making it the correct choice.