去年我们游览过长城
Last year we had looked around the Great Wall
昨天我们游览了长城
Yesterday we looked around the Great Wall
我们已经游览了长城
We have looked around the Great Wall
明天的计划是游览长城
The plan of tomorrow is look around the Great Wall
因为去年去是和现在这个时间点有一段时间段,是曾经发生的事.所以用过.
而昨天和现在时间属于一个时间段,一般过去时,用了.