单项选择题

It remains a puzzle about why our outermost planet exists.

A. problem
B. mystery
C. question
D. point
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单项选择题
It is not clear whether the increase in reports is stemmed from greater human activity or is simply the result of more surveys.
A. flows
B. comes
C. derives
D. originates
单项选择题
The majority of people around here are decent people.
A. honest
B. rich
C. good- looking
D. high- ranking
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