Answer: C) life becomes too difficult.
The speaker of the poem dreams of climbing trees in the following lines:
So was I once myself a swinger of birches.
And so I dream of going back to be.
It’s when I’m weary of considerations,
And life is too much like a pathless wood
These lines show that the speaker dreams of going back to a time when he was a climber of trees, and when life was less complicated. He argues that sometimes life becomes like a wood without a path, and it is in those moments that he feels like going back to climbing trees.