Every object has natural frequencies of oscillation with which they will respond when deflected from equilibrium. The marching soldiers appear to have been marching at a pace such that their stomping boots drove the oscillation of the bridge at:

if i am correct, your answer choices are:

a. the temperature remains constant

b. the temperature increases at a constant rate

c. heat flows at a constant rate into the system

d. heat flows at a constant rate out of the system

e. no heat flows into or out of the system

if so, then the answer is e. no heat flows into or out of the system.