Most text book questions will have the answers embedded in the chapter, and the answers will pertain to the topic that they're talking about. So if that chapter was in regards to physical layer characteristics of two dissimilar networks, then they probably wouldn't be looking for an answer on linking two different layer 3 networks.
1. Linking two similar networks -- hub, but switch would be better. Linking two dissimilar networks -- router.
2. Some answers I've come across over the years -- cable length, susceptibility to EMI, security. Three types of cables -- how about four? UTP, STP, fiber, coax.