\(\sqrt{15}\)
\(\sqrt{13}\)
\(\sqrt{12}\)
\(\sqrt{14}\)
A regular hexagon can be conceptually divided into 6 equilateral triangles. A line connecting two opposite vertices of the hexagon is formed by the sides of two opposing equilateral triangles. Thus, its length is double the side length of the hexagon, which is 4 cm.

Line \( AD \) divides the hexagon into two equal halves and bisects angle \( D \), resulting in angle \( ADC \) being 60°.
The cosine formula is used to calculate \( AT \):
\[ AT^2 = 4^2 + 1^2 - 2 \times 1 \times 4 \times \cos 60^\circ \] Simplifying the equation yields: \[ AT^2 = 16 + 1 - 8 \times \frac{1}{2} \] \[ AT^2 = 17 - 4 \] \[ AT^2 = 13 \] Taking the square root of both sides gives: \[ AT = \sqrt{13} \]
The correct option is \( \boxed{(B): \sqrt{13}} \).