As a general rule, is it permitted to travel at 50 km/h on a motorway?

As a general rule, is it permitted to travel at 50 km/h on a motorway?
A)Yes, as it is the minimum permitted speed.
B)No, you must travel at a minimum of 100 km/h.
C)No, you must travel at a minimum of 60 km/h.Correct
No driver shall impede the normal progress of other vehicles by travelling, without justified cause, at an abnormally reduced speed, which on a motorway or dual carriageway is considered to be any speed below 60 kilometres per hour.