作业帮she has been skating for 3 hou
来源：学生作业帮 编辑：作业帮 分类：英语作业 时间：2024/05/22 10:24:39
she has been skating for 3 hours,but he juse started an hour ago.
为什么用an hour ago而不用for an hour?
为什么用an hour ago而不用for an hour?
解题思路： 解答此问题的关键是弄清楚一般过去式与现在完成时及延续性动词与终止性动的用法
解题过程：
for与表示一段时间的词组连用，常用于现在完成时，表示过去已经开始，持续到现在的动作或状态。for所在句子中的动词是延续性动词。如：
I’ve lived in China for 2 years.
I’ve know him for more than 20 years.
an hour ago一小时之前的时间点，用于过去时。句中start是终止性动词。终止性动词，一般不能与“for…”或“since…”等表示延续的时间状语连用。
解题过程：
for与表示一段时间的词组连用，常用于现在完成时，表示过去已经开始，持续到现在的动作或状态。for所在句子中的动词是延续性动词。如：
I’ve lived in China for 2 years.
I’ve know him for more than 20 years.
an hour ago一小时之前的时间点，用于过去时。句中start是终止性动词。终止性动词，一般不能与“for…”或“since…”等表示延续的时间状语连用。
Alison has been skating for five hours.
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