单项选择题

______ much is known about what occurs during sleep, the precise function of sleep and its different stages remains largely in the realm of assumption.

A．Because
B．For
C．Since
D．While
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单项选择题
All the tasks ______ ahead of time, they decided to go on holiday for a week.
A．had been fulfilled
B．were fulfilled
C．having been fulfilled
D．been fulfilled
单项选择题
______ in the office had made a mistake, and the firm regretted causing the customer inconvenience.
A．Some
B．Anyone
C．One
D．Someone
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