How do you interact with someone who doesn't ask questions?

My wife is the extreme case but I also run across these people in business. They make statements, some of them provocative like "Look at that!" or others are just mysterious like "Bob bought a car yesterday". It leaves me wondering how to respond.

Should I:

a) Say nothing, because I have nothing to say

b) Say something diffuse to show interaction without causing any problems. Such as "Oh, interesting" followed by "I've heard of people doing that" etc.

c) Try to figure out what the other person really wants to hear, and respond with a question such as "Oh, would you like a new car too?" to help them draw out their feelings.

d) Say what is honestly on my mind, such as "That's ridiculous" or "Why were you even talking to them"?