[ Grammar ]
Electron storage rings ___ in investigations of the structure of materials.
A. They are used
B. That are used
C. Used
D. Are used

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I ____ to bed before 12:00
A. don’t never go
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B. They are having dinner.
C. They will be having dinner.
D. They had dinner.
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It is important ____ people back right away
A. calling
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