Agirl who is watching a plane fly tells her friend that the plane isn't moving at all. describe a frame of reference in which the girl's description would be true.

She's riding inside the plane, moving at the same speed as the plane, which means the plane is not moving relative to her since they're moving together.

It's the same case riding a bike, driving a car, boating, etc. . . . you're moving with the object.

Iwould say a is accurate