A circle has a radius of 4 \mathrm{~cm}. A line segment joins two points on the circle. What is the greatest possible length of the line segment?
Answer Choices
A. 10 \mathrm{~cm}
B. 8 \mathrm{~cm}
C. 4 \mathrm{~cm}
D. 12 \mathrm{~cm}
E. 6 \mathrm{~cm}