Q. Read the extract given below and answer the question that follows:
When I casually mentioned this to a friend, he casually replied that I had better get one in the Tigris marshes, for there they were as common as mosquitoes, and were often tamed by the Arabs. We were going to Basra to the Consulate-General to collect and answer our mail from Europe. At the Consulate-General we found that my friend’s mail had arrived but that mine had not.
What was 'they' ?