If a string vibrates at the fundamental frequency of 528 Hz and also produces an overtone with a frequency of 1,056 Hz, this overtone is the 

A. second harmonic.

B. first harmonic.

C. fourth harmonic.

D. third harmonic.

1. The _______ of a sound wave is defined as the amount of energy passing through a unit area of the wave front in a unit of time. 
   

A. amplitude

B. compression

C. intensity

D. frequency