D doesn't make much sense, it's valid, but not what we're looking for. B also has a correlation with D, same reasoning applies. As for A, it seems pretty legit, but I don't believe that's what we're looking for.
Choice C is the most obvious one though. We're talking about a network and as may or may not know it's a wireless one in a manner of speaking. A couple of computers in the network that have trouble maintaining a signal will indefinitely lead to failure of a network since both the links and nodes of certain computer systems are incapable of maintaining a signal.
