20. What is the speed of electron with kinetic energy of 1.5 MeV (without including the rest mass energy of m_ec² = 0.5 MeV)? Here c = 3.0 × 10⁸ m/s is the speed of light.
(A) 1.5 × 10⁸ m/s
(B) 2.0 × 10⁸ m/s
(C) 2.5 × 10⁸ m/s
(D) 2.8 × 10⁸ m/s
(E) 3.0 × 10⁸ m/s

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