When a tuning fork vibrates over an open pipe and the air in the pipe starts to vibrate, the vibrations in the tube are caused by ... A. ResonanceB. HarmonicsC. ReinforcementD. Beats

correct option is A. Resonance

Explanation:

solution

vibrations in the tube are caused by the Resonance because Resonance cause of sounds production in the musical instrument

As if resonance (hollow cylindrical tube) immerse in cylinder of water and force in to vibration by tuning fork

As tines of tuning fork vibrate at natural frequency and it create sound wave that impinged up on opening of resonance tube

so correct option is A. Resonance