【B19】
A. pace
B. looking
C. abreast
D. time
Security and commodity exchanges are meeting places for buyers and sellers of____.
A. stocks
B. securities
C. products
D. all of the above
【B15】
A. questionable
B. little
C. retorted
D. accurate
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.
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