The third one is the most correct, although perhaps a little terse.
The basic idea here is that light waves (all electromagnetic waves, in fact) are coherent excitations of the electric and magnetic fields. In vacuum, they travel through space at c. However, one thing about electric and magnetic fields is that they cause charges to move around; and one thing about moving charges is that they throw off electromagnetic waves of their own.
So when an electromagnetic wave happens upon a material object, made up of charged particles (electrons and protons) that are bound together by complicated force structures of their own, the picture on the microscopic level becomes very complicated. The impinging electromagnetic field causes the charges to move from their equilibrium positions, which causes the charges to radiate electromagnetic fields of their own, whose forces add on to the forces that the impinging wave is causing, which… and so on and so on. It turns out that the only way for these forces and fields to act like a wave inside the material is for them to travel at a speed somewhat less than c; otherwise, the charges in the material end up oscillating out of phase with the initial wave, the resultant radiation interferes with itself and the impinging wave, and the resulting configuration of fields looks nothing like a coherent wave travelling through the medium. Only by having a coherent oscillation of material and external wave can you get something that walks like a wave and quacks like a wave.
All this is on the level of classical electrodynamics, by the way. Things can be explained in terms of quantum mechanics as well (this is where the “polaritons” the Wiki article mentioned come in — they’re the analog of photons in vacuum), but it gets very complicated very quickly and to be honest I don’t entirely understand it myself. Unless some brave & gifted physics teacher happens upon this thread to explain that to you, you’ll probably have to make do with the classical picture; it’s pretty darn accurate anyhow, so don’t worry that you’re somehow being short-changed.