听力原文： We cannot feel speed. But our senses let us know that we are moving. We see things moving past us and feel that we are being shaken. We can feel acceleration, an increase in speed. But we notice it for only a short time. For instance, we feel it during the take-off run of an airplane. We feel the plane's acceleration, because our bodies do not gain speed as fast as the plane does. It seems that something is pushing us back against the seat. Actually, our bodies are trying to stay in the same place, while the plane is carrying us forward.
Soon the plane reaches a steady speed. Then, because there is no longer any change in the speed, the feeling of forward motion stops.
How do you explain that we are moving？

A. By watching things move past.
By feeling the speed.
C. By feeling ourselves being shaken.
D. Both A and C.