2. (b) (5 points) What is the definition of an infinite set $W$?

(c) (5 points) Let $N$ be the set of natural numbers. Assume that we already know $N$ is an infinite set. Let $S = \{k/2^n \mid n = 0,1,2,\ldots; k \in N\}$. Note that $/$ in this question is the division of real numbers. For example, $5/2 = 2.5$. Prove that $S$ is an infinite set strictly according to your definition of an infinite set.