时态的运用过去时和过去完成时

2 时态的运用过去时和过去完成时

老师好，

请看下面一段话，这段话被我修改过了，但是我不确定里面过去完成时和过去时的正确性，请老师指教

Peru’s culture ministry says the cat wasn’t seen before because it’s on a very steep hill. The picture had almost disappeared because of erosion. Parts of the drawing were worn away by natural forces, such as wind and water. The drawing has been cleaned up and will be preserved.