Can someone please explain the (c) part of the answer?
What I understood is that the concatenation with an empty set results in the empty set(phi) and which is the part of every set, so this confirms that L can be anything. My doubt is how can we say that L/L' should be an empty string, but it can be anything.
According to the definition which I understood L/L' contain all the strings w which are the prefix to some string x which belong to L' and the concatenation of w and x belongs to L.