Near Coevorden you are on a road with an 80 km/u limit, behind a tractor doing about 35 km/u. You wonder whether that speed is allowed. How do you judge it?
Too fast: an agricultural vehicle may drive at most 25 km/u here
That is allowed: like you, it may simply drive 80 km/u here
That may be right: some agricultural vehicles may drive up to 40 km/u
Explanation
False — you think every agricultural vehicle may do at most 25 km/u. Some agricultural vehicles may do at most 25 km/u, others at most 40 km/u; you cannot tell which from the vehicle (Book p.131).