Let $A \in M_{n \times n}(\mathbb{C})$. Which of the following statement(s) is/are true?\\
(A) There exists $B \in M_{n \times n}(\mathbb{C})$ such that $B^2 = A$.\\
(B) $A$ is diagonalizable.\\
(C) There exists an invertible matrix $P$ such that $PAP^{-1}$ is upper-triangular.\\
(D) $A$ has an eigenvalue.