单项选择题

Sulfur has occasionally been found in the earth in an almost pure state.

A．regularly
B．accidentally
C．sometimes
D．successfully
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单项选择题
You have to follow the guide whose sole interest is to cover all spots according to his strict schedule.
A．obvious
B．simple
C．only
D．assumed
单项选择题
He expressed concern that the ship might be in distress.
A．despair
B．difficulty
C．need
D．danger
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