Answer:
[tex]\large\boxed{A.\ \sqrt{-4}}[/tex]
Step-by-step explanation:
[tex]A.\ \sqrt{-4}=\sqrt{(4)(-1)}=\sqrt4\cdot\sqrt{-1}=2i\ -\ \text{complex number}\\\\i-\text{imaginary unit}[/tex]
[tex]B.\ \sqrt{13}\approx3.61\ -\ \text{real number}\\\\C.\ \sqrt{16}=4\ -\ \text{real number}\\\\D.\ \sqrt1=1\ -\ \text{real number}[/tex]
