单选题 Questions 18 to 21 are based on the following passage.

单选题 How do you explain that we are moving?

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

【正确答案】 D

【答案解析】[解析] 题干问：“你如何解释我们是正在运动的?”听力材料中说“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.”即，我们可以通过观察周围物体的运动和感觉我们自己的颤动来知道我们正在运动。所以本题的答案选D。

单选题 How do we feel during the take-off run of a plane?

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.

【正确答案】 B

【答案解析】[解析] 题干问：“飞机起飞的时候，我们感觉怎么样?”听力材料中说：“It seems that something is pushing us back against the seat.”这和答案B的意思一致，所以本题答案选B。

单选题 Why do we feel the plane"s acceleration?

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.

【正确答案】 C

【答案解析】[解析] 题干问：“我们为什么能感觉到飞机的加速?”从听力材料“We feel the plane"s acceleration, because our bodies do not gain speed as fast as the plane does.”可知，答案选C。

单选题 When does the feeling of forward motion stop?

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.

【正确答案】 C

【答案解析】[解析] 题干问：“什么时候能感觉到向前运动停止了?”对话材料最后说：“Soon the plane reaches a steady speed. Then, because there is no longer any change in speed, the feeling of forward motion stops.”该句的意思与答案C的意思一致。