Given this transition system, for which states are these (very basic) LTL formulas fulfilled?

Question

I missed a lot of lectures for this module due to surgery so I'm trying to teach it to myself now. This is the question I've been working on:

First of all, would I be correct in saying that the LTL formulas are b, c and e? CTL are a, d and f?

For (b) I'm guessing the answer is s1 and s3, since those are the only states with b in them.

Looking at (e), this says that the state must always contain b or a, so the answer is s1, s2, s3 and s4 (all states). Is this correct?

(c) is the one I can't get my head round. What exactly is it saying in english?

For now I'll just focus on the LTL stuff, so I just want to get b, e and c 100% correct. Any help is highly appreciated since I'm struggling a bit with this module.

Many thanks in advance!