19. A park is in the shape of a regular hexagon with each side 2 kilometers long. Alice starts from a corner and walks 5 kilometers along the park's perimeter. How far is she from her starting point?
(A) $\sqrt{13}$;
(B) $\sqrt{14}$;
(C) $\sqrt{15}$
(D) $\sqrt{16}$;
(E) $\sqrt{17}$
19
A
19. As shown in the figure, let's assume Alice starts from point $A$ and reaches point $B$. By the cosine rule, we get $A C=2 \sqrt{3}$. In $\triangle A B C$, $\angle A C B=90^{\circ}$. By the Pythagorean theorem, we have
$$
(A B)^{2}=13, A B=\sqrt{13} .
$$