The colony in Hive C is dead. It appears to have starved because of the extended cold during March.
I visited my out apiary today to see that the bees were ok. Two of the 3 hives which I thought occupied were flying. The other was too quiet. I suited up and found bees inside which were in the last stage of starvation before death.
There were still some stores in the hive but it appears to have been too hard, or too remove from the cluster, to access. There is still capped brood in there, showing that there was a laying queen during some part of March. I think that the last 2 or 3 cold nights must have finished them off. The Queen probably stopped laying during the cold spell around 16th March. It has been fairly cold since, with only short periods above 10C (minimum flying temperature) during the last week.
This is a disappointment. I thought that this colony was a survivor.