Step 1: Recall natural running biomechanics.
In running, when one leg is forward, the opposite arm swings forward to balance. Legs move in opposite directions, and arms counterbalance them.
Step 2: Examine options.
- (A): Both right arm and right leg forward – unnatural.
- (B): Left leg forward, right arm forward – correct natural pose.
- (C): Both arms positioned unnaturally with legs – incorrect.
- (D): Crouched pose with wrong balance – not natural running.
Step 3: Conclude.
Option (B) shows proper opposite arm–leg coordination.
Final Answer:
\[
\boxed{B}
\]