Question id 420 - General Navigation - ATPL - Airline Transport Pilot license

Morning civil twilight is the period in the morning from the centre of the Sun is 6° below the horizon until the upper limb of the Sun appears at the horizon.
The period of semi-darkness in morning.
The period when the Sun, in the morning, has its centre between 6° under the horizon and the horizon.
The period in the morning, just before sunrise.