Aşağıdakilerden hangisi boş kümedir?
A) $\left\{x : x^2 = 0, x \in \mathbb{R}\right\}$
B) $\left\{x : x^2 + 1 = 0, x \in \mathbb{R}\right\}$
C) $\left\{x : x > 5, x < 10, x \in \mathbb{Z}\right\}$
D) $\left\{x : x + 2 = 5, x \in \mathbb{Z}\right\}$
E) $\left\{x : 2x = 4, x \in \mathbb{Z}\right\}$
