When driving in a tunnel, what safety distance must we maintain with the vehicle in front of us?

When driving in a tunnel, what safety distance must we maintain with the vehicle in front of us?
A)At least 150 metres.
B)At least 100 metres.Correct
C)At least 50 metres.
In tunnels or underpasses, when not intending to overtake, a safety distance with the preceding vehicle of at least 100 metres or a minimum time interval of four seconds must be maintained at all times.
For vehicles with a MAM of more than 3,500 kg, the safety distance to keep will be at least 150 metres or a minimum interval of 6 seconds.
Remember that overtaking is prohibited in tunnels, unless we have more than one lane in our direction.
The following sign reminds us of the general safety distance we must keep.