Because of the 'hint' that 'the action was completed' I changed my initial answer from 'Ce Noel etait' to 'Ce Noel a ete' - but I find it's 'etait' in the above version.
I also had used the word 'etincelantes' but this was scored out and replaced with 'brillantes'.
This is by no means the first time that similar things have happened and I'm a bit peeved that I've had to mark myself down needlessly.