People who stop you while you run!!

Would someone please tell me how to be polite to people who try and stop me to talk when I'm out for my run, so far the only thing I have figured out to do is stop and talk to them for fear of being rude. I really hate it though when people stop me because it breaks my rhythm. I kinda get into my own world when I'm out running and the only thing I let it is cars because I don't want to get hit. I will say that if I'm running with someone its cool I can hold a conversation and it doesn't bother me but the stopping because someone wants to know how far I'm running or something like that just gets to me. I don't know maybe I'm being silly if I am please tell me. Anyway I got in 71/2 miles today even with the rain.