A car is travelling on a conventional road — when will its speed be considered abnormally reduced?

A)When it is less than 60 km/h.
B)When it is less than 40 km/h.
C)When it is less than 45 km/h.Correct
When travelling at a speed lower than the minimum permitted speed, one is travelling at an abnormally reduced speed.
In the case of conventional roads, with a maximum speed of 90 km/h, the minimum will be 45 km/h — half the maximum — and therefore a speed below 45 km/h will be considered abnormally reduced.
Minimum speeds must be observed just as maximum speeds must, even if there is no specific sign indicating them.
The minimum on motorways and dual carriageways is 60 km/h, while on all other roads it is half their maximum speed.