单项选择题

Data from Voyager II have presented astronomers with 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
The river was contaminated with waste.
A．blackened
B．polluted
C．widened
D．mixed
单项选择题
She tried to probe my mind and discover what I was thinking.
A．solved
B．explored
C．involved
D．exploded
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