A particle is found to be at rest when seen from a frame S₁ and moving with a constant velocity when seen from another frame S₂ . Choose the possible options

S₁ is moving with constant velocity w.r.t frames S₂  . So, if S₁ is inertial, then S₂ will be inertial and if S₁ is non-inertial, then S₂ will be non-inertial.

Assume one inertial frame in which particle is at rest. Let it be frame S₁ ​ , and second frame S₂ ​ , which is moving with constant velocity. For frame S₂ ​ , particle will now be seen moving with constant velocity. So, Option A is correct. 

Now assume frame S₁ ​ and frame S₂ ​ are non- inertial frames moving in same direction with same acceleration as that of particle. Now, assume at this moment, velocity of particle and frame S₁ ​ is same, so particle will be seen at rest from frame S₁ ​ . Now, for same moment of time, let frame S₂ ​ have different velocity than particle, so from frame S₂ ​ particle will now be seen as moving with constant velocity. So, option B is also correct.