At what distance from a tunnel is overtaking forbidden?

1. AThere is no restriction on overtaking in the vicinity of a tunnel.
2. BFrom 50 metres before the entrance to the tunnel until 50 metres after the exit from it.
3. CFrom the entrance to the tunnel until the exit from it.
4. DFrom 100 metres before the entrance to the tunnel until 100 metres after the exit from it.

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