Step 1: Compare slopes
The objective line $5x+10y=c$ has the same slope as $x+2y=10$.
Step 2: Conclude
So the objective line coincides with that edge when $z=50$, and every point on that edge is optimal. The edge runs between $(0,5)$ and $\left(\tfrac{14}{5},\tfrac{18}{5}\right)$, option (D).
Final Answer:
Option (D) names the optimal segment.
\[ \boxed{(0,5)\text{ to }\left(\dfrac{14}{5},\dfrac{18}{5}\right)} \]