What is a key characteristic of the butterfly stroke?

• A. It requires strength and body undulation, with both arms moving symmetrically.
• B. It uses alternating arm strokes with irregular timing.
• C. It relies on a rigid body with no undulation.
• D. It is performed on the back.

Answer: (A)

Butterfly relies on a strong, coordinated wave-like motion through the body and a symmetric arm action. Both arms move together in the same moment, pulling simultaneously through the water before they recover in unison, while the hips and chest undulate to help drive propulsion. This combination of simultaneous arm movement and body undulation is the defining feature that makes butterfly unique and effective.

The other descriptions fit other strokes or principles: alternating, irregular arm timing is more characteristic of freestyle; using a rigid body with no undulation would not generate the necessary propulsion in butterfly; and performing on the back describes backstroke, not butterfly.