核心问题
The rainy season lasts for six months and water gets in among the stones. 查《新英汉词典》和《最新高级英汉词典》，last 的时间状语，如果是名词短语，其前是不加介词 for 的： The performance lasted two hours. 演出持续了两小时。
词典解答
last 不管用作及物动词还是不及物动词,其后的介词 for 是可有可无的:
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The concert lasts two hours. 音乐会持续了两个小时。
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The haymaking lasted (for) a week. 晒干草用了一周的时间。
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The meeting lasted two hours. 会议开了两小时。
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The drought lasted for several months. 干旱持续了几个月。
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The war lasted (for) five years. 战争持续了五年。
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This was the American Civil War, which lasted four years. 这就是美国内战，延续了四年之久。
练习题
请做下面的英语试题：
It was the largest experiment we have ever had; it ____ six hours.
A. ended B. finished C. was D. lasted