What causes the ocean roar (waves) one may hear in a seashell? .
A. Actually, there is no roar. The sound entering one ear is muffled, and we 'sense' that as a roar.
B. The roar is due to the shell's cavity acting as an amplifier for blood pulsing in our veins.
C. The roar is due to wind and vibrations randomly exciting the shell's resonant frequencies.