Use the Trigonometric Substitution to Rewrite the Algebraic Expression as a Trigonometric

Use the trigonometric substitution to rewrite the algebraic expression as a trigonometric function of θ,where $0 < x < \frac { \pi } { 2 }$ .​ $\sqrt { 16 - x ^ { 2 } } , x = 4 \cos \theta$ ​

A) 16 cos θ
B) 16 sin θ
C) 4 sin θ
D) - 4 sin θ
E) 4 cos θ