Which of the Following Is True Regarding Harmonic Tremors

Which of the following is true regarding harmonic tremors?

A) they are associated with the sharp release of energy when two pieces of land move against each other,as along a fault.
B) they are produced by sub-surface movement of magma beneath a volcano.
C) they are associated with movements in the crust caused by cities and traffic.
D) they are produced by explosive volcanic eruptions.
E) they are audible from the surface as a high pitched noise that indicates that the eruption is imminent.