研究者给一些家庭送了一套游戏软件，另一些家庭则只有在完成了四个月的学习任务后才送游戏软件。
Researchers gave some families a game system; other families were promised a system when the four-month study ended.
研究者给一些家庭送了一套游戏软件，另一些家庭则只有在完成了四个月的学习任务后才送游戏软件。
Researchers gave some families a game system; other families were promised a system when the four-month study ended.
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