Whether we realize it or not(Para. 3), "it" refers ______.
A. weightlessness
B. the continuous and universal nature of gravity
C. the fact that our bodies never forget
D. the previous statements
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The tree was cut ______.
A. down
B. in
C. off
D. ont
According to the passage we do not perceive gravity because ______.
A. we live in a downward-pulling world
B. there is no decrease or increase force of gravity on our bodies
C. our senses provide accurate information about the location
D. our brains integrate signals from all apparatus of the body
听力原文：W: I think that the best time to retire from work is around 60.
M: Well, if people are still healthy, why must they stop work？
Q: What are the two speakers talking about？
(7)
A. Retirement age.
B. Old people's health.
C. Keeping health.
D. Old people's salary.
The purpose of the author in writing the text is to ______.
A. introduce the Amazon River
B. illustrate some facts about Amazon River cultures
C. show the present situation of Amazon River
D. compare the differences between world cultures
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