A person sitting still in a moving airplane is considered to be... (SP1a) a. Motionless in relation to everything in the plane. B. In motion compared to everything on the ground. C. Both a and b. D. Neither a nor b.

C. Both a and b

Explanation:

Firstly, persons and objects in a moving plane as described in this question, are moving at the same speed as the plane even if there is no individual movement of these objects.

However, this question describes a person sitting still in a moving plane. This means that;

- The person is motionless in relation to everything in the plane i.e the person is not moving even if other things in the plane are.

- The person is in motion compared to everything on the ground i.e. the person is moving at the same speed as the plane, hence, in comparison with the ground, the person is moving.

Therefore, options A and B are correct