Find the Value of N So That the Expression Is $$x ^ { 2 } + 20 x + n$$

Multiple Choice

Find the value of n so that the expression is a perfect square trinomial and then factor the trinomial. $$x ^ { 2 } + 20 x + n$$

A) $n = 100 ; ( x + 10 ) ( x - 10 )$
B) $n = 100 ; ( x + 10 ) ^ { 2 }$
C) $n = 400 ; ( x + 20 ) ^ { 2 }$
D) $n = 100 ; ( x - 10 ) ^ { 2 }$