Why can the hummingbird hover and even fly backwards？
A. Because its wings are large enough.
Because it can tilt its body.
C. Because it has whirling and horizontal blades like a helicopter.
D. Because it can produce down-draft of air by beating their wings very fast.
Which of the following is the reason for the Crash in 1929？
A. High taxation for trade.
B. Tricks of some businessman.
C. Speculation of some people.
D. Strict regulation of the state.
The first known census report took place in Babylonia in_____.
A. 1085
B. 1200 B.C.
C. 3800 B.C.
D. 1790
The American census today costs the government approximately_____.
A. $ 0. 0/person
B. $ 0. 10/person
C. $1. 00/person
D. $ 10. 00/person
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