What must we do in view of the sign?

What must we do in view of the sign?
A)Turn off the low-beam lights.
B)Mandatorily use the low-beam or high-beam lights.
C)Keep the dipped beam lights on if visibility circumstances so require.Correct
This sign indicates the end of the obligation to use low-beam lights imposed by a previous sign.
In any case, if visibility circumstances so require, for example at night, we must keep the lights on.