飞机正常飞行15分钟后警示灯开始闪烁。
The plane was flying normally for about 15 minutes before a warning light blinked on.
一盏灯每晚七点钟亮。
读者文摘解答：如果是白炽灯，每次只要你离开房间超过5秒钟就要关掉；如果是节能灯，超过15分钟的话一定要记得关。
Reader's Digest Version: Turn off incandescents if you're leaving the room for more than five seconds; CFLs, if you'll be gone at least 15 minutes.
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