This 15-year-old boy ____________________________ (应该懂事了,不该整天玩电脑游戏).
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___________________________________________(这项政府工程的目的) is to ensure food safety.
_______________________________ (充足的电力供应) is necessary for economic development.
__________________________________ (你必须记得把文件保存下来) before you turn off the computer.
______________________________________ (你无论在什么情况下都不可告诉他) what has happened.