Which best states the overall structure of walden?

Many experts find it difficult to states overall structure of walden since it has no clear story line or plot.

According to them, the best way to state overall structure of walden is that  Thoreau uses a haphazard and unplanned approach detailing only significant events on his journey

hope this helps

Ithink it's a. but i could be wrong because it might be b. but it's not the other two