This sign prohibits...
A)the passage of vehicles less than 4.5 metres wide, including load.
B)the passage of all vehicles when their load protrudes from the sides.
C)the passage of vehicles more than 4.5 metres wide, including load.Correct
The sign in the question prohibits the passage of vehicles whose maximum width, including load, exceeds that indicated.
Other related signs:
(All 3 signs apply to all vehicles)