I wish to refer to someone's mum out of a group of people, but without specifying the individual.<br/><br/>Do I say:<br/><ul><br/><li>"I spoke to one of their mums"</li><br/><li>"I spoke to one of their mum"</li><br/><li>"I spoke to the mum of one of them"</li></ul>I prefer one of the first two as the last one is conjunctive.<br/><br/>Any ideas?