In the First Law of Thermodynamics, the Change in Internal

In the first law of thermodynamics, the change in internal energy ΔE_int:

A) is always positive
B) is always negative
C) cannot be zero
D) tends to increase if heat energy is transferred to the gas, and tends to decrease if the gas does work on its environment
E) tends to decrease if heat energy is transferred to the gas, and tends to increase if the gas does work on its environment