单项选择题

Nowhere in nature is aluminum found free, owing to its always ______ with other elements, most commonly with oxygen.

A．being combined
B．having combined
C．to combine
D．combined
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单项选择题
Mary will not be able to come to the birthday party as she is ______ with a cold.
A．laid out
B．laid up
C．laid by
D．laid down
单项选择题
It was requested that all of the equipment ______ in the agreed time.
A．erected
B．would be erected
C．be erected
D．will be erected
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