17. Which of the following statement is not true about the theory of relativity? (A) Two events A and B occur at different locations. In some frame, event A occurs before B. There must exist another frame where event B occurs before A. (B) Photons do not have rest mass but their trajectories can be bended by gravity. (C) A clock in an accelerated frame ticks slower than one in an inertial frame supposing that the two clocks are identical in the same frame. (D) The kinetic energy of a particle of rest mass m₀ and velocity v is m₀c², where c is the speed of light in vacuum.

9. In a model gasoline engine, the air-gasoline mixture can be treated approximately with a thermodynamic cycle known as the Otto cycle. In the first process (1→2), the gas undergoes an isentropic compression (the engine's compression stroke), during which the temperature rises from 300 K to 600 K. The next process (2→3) is an isochoric pressure increase, and the gas temperature reaches 1500 K as the gasoline burns. Next (3→4), the gas undergoes isentropic expansion (the engine's power stroke) during which its temperature drops to 800 K. Finally (4→1), the gas experiences an isochoric pressure decrease during which its temperature drops back to 300 K. Please estimate the efficiency of this model engine. (A) 10%~20% (B) 20%~30% (C) 30%~40% (D) 40%~50%.

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