英语时态：我去过长城,觉得长城很大.The Great Wall is/was very big,请问这里的时态怎么用?

其实这里不存在客观事实描述的问题,因为你翻译为“我觉得”长城很大,还是属于一种主观感受,除非就是简单的长城很大,The Great Wall is very big.
否则
I have been to The Great Wall and I think it is very big.
这是去过之后的感想,但也有这种情况,Once i went toThe Great Wall and I thought it was very big.一个指当时的感受,一个指去过之后的感想.