Near Heerenveen you drive through fog in the morning. You can see about 80 metres: limited, but not yet below 50 metres. What do you do?
Switch on my front fog light and drive on, because then others see me
Drive on with a 2-second gap; adjusting is only needed below 50 metres
Lower my speed now and keep more distance than in good visibility
Explanation
False — You wait to adjust until the 50-metre limit. When fog forms you adjust your driving straight away; below 50 metres of visibility you even keep three instead of two seconds of distance (Book p.190-191).