About The seven categories of traffic signs (appendix 1): which statement is WRONG?
F1 is listed literally under 'Other commands and prohibitions', not under chapter C 'Closure'.
The priority-road sign (B1) is a triangle, just like a warning sign.
Command signs (round, blue) are a separate category from category C (round, red border).
Road users are required to comply with traffic signs that contain a command or prohibition.
Explanation
trap: shape confused with another category. B1 (priority road) has its own yellow diamond shape, not a triangle. The triangle with a red border is the appearance of category J (warning)