Pick up the correct statement from the following:

• Duty of canal water is defined as the total area irrigated by the discharge averaging one unit during the base period of the duty
• Duty of canal water is usually calculated at the head discharge of a channel
• Duty of canal water at the head of a channel and at the outlet of a distributary, differ considerably due to progressive losses of water
• Duty of canal water at the outlet of a distributary, is generally known as outlet factor or outlet discharge factor
• All the above.