Find the Missing Monomial, Factor or Term $(?)^{2}=x^{2}+16 x+64$ A) $x^{2}+8$ B) $x+8$

Find the missing monomial, factor or term.
- $(?) ^{2}=x^{2}+16 x+64$

A) $x^{2}+8$
B) $x+8$
C) $x-8$
D) $-x+8$