Which of the following statements are evidence that gases do not always behave ideally? -At 4 K and 1 atm, helium is a liquid. -When two gases are mixed, they follow Dalton\'s law of partial pressures. -It is impossible to compress a gas enough so that it takes up no volume. -CO2 gas becomes dry ice (solid CO2) at 1 atm and -78.5 °C.