2. Which of the following quantities is invariant under Lorentz transformation? (A) Length (B) Time (C) Energy (D) Momentum (E) Mass

7. Which of the following statements about superconductivity is correct? (A) All materials become superconducting below 30 K (B) The resistance of a superconductor is zero (C) Superconductivity violates the first law of thermodynamics (D) Superconductivity violates the second law of thermodynamics (E) All the above are incorrect