Answer:
B. equals zero
Explanation:
Given data
one complete cycle = heat flow
solution
we have given that when heat engine complete 1 cycle change in energy = net heat flow
that is always equal to zero
from first law of thermodynamics that
ΔU = Q + W
we know ΔU is the change internal energy in system and Q is net heat transfer in system and W is  net work done in system
therefore change of internal energy during one cycle
ΔU = Ufinal -  Uinitial
ΔU  = Uinitial  -  Uinitial  = 0