How many of the following statements is/are correct?

(a) Let $A = \{x : 1 < x < 2,\, x \text{ is a natural number}\}$. Then $A$ is the empty set, because there is no natural number between $1$ and $2$.

(b) Let $B = \{x : x^2 - 2 = 0 \text{ and } x \text{ is a rational number}\}$. Then $B$ is the empty set because $x^2 - 2 = 0$ is not satisfied by any rational value of $x$.

(c) Let $C = \{x : x \text{ is an even prime number greater than } 2\}$. Then $C$ is the empty set, because $2$ is the only even prime number.

(d) Let $D = \{x : x^2 = 4,\, x \text{ is odd}\}$. Then $D$ is the empty set, because $x^2 = 4$ is not satisfied by any odd value of $x$.