Answers (E) must be wrong because the relationship between and cannot depend on inertial frame . Answers (C) and (D) must be wrong. This can be seen from the case when inertial frame and are moving with equal speeds in opposite directions, relative to th inertial frame . Then the average lifetime in them must be equal, which it is not according to answer (C) or answer (D). To select between answers (A) and (B), recall that ``moving clocks run slow" and that is the factor that relates time differences in two inertial frames. This implies that answer (B) is correct.
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