What does this sign mean?

What does this sign mean?
A)Minimum separation.Correct
B)Traffic congestion.
C)Overtaking prohibited.
When driving behind another vehicle, you must leave a space that allows you to stop, in case of sudden braking, without colliding with it, taking into account the speed and the conditions of grip and braking. In addition, if you are driving without signalling your intention to overtake, this separation must allow the vehicle behind you to overtake safely.
This sign reminds us, in a general way, that we must always keep this safety distance between vehicles. If it also includes an indication of distance in metres, that would be the distance we should maintain (Image 1)
For these purposes, drivers of vehicles with more than 3,500 kg of MAM and vehicles and combinations of vehicles more than 10 metres long must keep a minimum separation of 50 metres.
It will be sufficient to maintain a distance to avoid collision (no need to keep distance to allow others to overtake):
- In built-up areas.
- Where overtaking is prohibited.
- Where there is more than one lane in the same direction.
- When traffic is congested.
- When you intend to overtake.

In tunnels and underpasses we must maintain a safety distance with the preceding vehicle of at least 100 metres or 4 seconds. Vehicles with more than 3,500 kg of MAM, 150 metres or 6 seconds.