Suppose You Are in a Jet Airliner Traveling at a Constant

Suppose you are in a jet airliner traveling at a constant speed of 400 km/h in a constant direction.All windows are blocked,so you cannot see outside,and there are no vibrations from the engines.What experiment can you do to determine that you are in fact moving?

A) Suspend a ball by a thread from the ceiling and measure the angle the thread makes with the vertical.
B) None-all experiments will give the same results that you would get when at rest on the ground.
C) Measure the speed of a sound wave traveling up the aisle (toward the nose of the aircraft) and another traveling down toward the tail, and calculate the difference between the two results.
D) Drop a small rock and measure the distance it moves backward down the aisle as it falls.