(1)
A)By watching things move past.
B)By feeling the speed.
C)By feeling ourselves being shaken.
D)Both A and C. (2)
A)That we are being thrown forward.
B)That we are pushed back against the seat.
C)That we are lifted out of the seat.
D)That we are pushed down into the seat. (3)
A)Because our bodies gain speed just as fast as the plane.
B)Because our bodies do not gain speed.
C)Because our bodies gain speed more slowly than the plane.
D)Because our bodies gain speed before the plane. (4)
A)When the plane stops climbing.
B)When the plane lands.
C)When there is no longer a change in speed.
D)When we begin to feel speed.
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 speed, the feeling of forward motion stops.
How do you explain that we are moving?
How do you feel during the take—off run of a plane?
Why do we feel the plane’s acceleration?
When does the feeling of forward motion stop?