Pick up the correct statement from the following :

• The unit hydrograph of a specified unit duration obtained from the past data can be used to obtain the hydrograph of future storms of like duration
• To obtain the ordinates of storm hydrograph, the ordinates of unit hydrograph are multiplied by the multiplying factor
• The multiplying factor for storm hydrograph may be obtained by dividing the run off in mm by 25 mm
• A tolerance of about 25% of specified duration of unit hydrograph may be accepted without any serious error
• All the above.