微机上广泛使用的WindowsXp是______。
A. 多用户多任务操作系统
B. 单用户多任务操作系统
C. 实时操作系统
D. 多用户分时操作系统
Some pictures of the river brought the days back to the old ________ they swam in it.
A. when
B. that
C. who
D. where
The man showed us so heavy a stone ________ no man can lift.
A. that
B. as
C. which
D. what
He stayed there for quite a long time, during ________ time he learned much spoken English.
A. that
B. this
C. which
D. same
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