A quarter-circle slice is cut out from a circular piece of paper with radius 8 units. The remaining part is joined together as shown in the figure with the red lines coinciding to form a right circular cone.
Accordingly, what is the height of the formed cone in units?\\
A) $2 \sqrt { 3 }$\\
B) $2 \sqrt { 5 }$\\
C) $2 \sqrt { 7 }$\\
D) $3 \sqrt { 2 }$\\
E) $3 \sqrt { 3 }$