#### Answer

D.

#### Work Step by Step

$x=5\cos 38^{\circ}\implies \cos38^{\circ}=\frac{x}{5}$
But $\cos\theta=\frac{\text{adjacent side}}{\text{hypotenuse}}$
This implies that $x$ is the length of the adjacent side to the $38^{\circ}$ angle and the length of the hypotenuse is 5. This is the case in triangle D.