Which element of the romantic movement is present in this excerpt from the "The Solitary Reaper" by William Wordsworth?

Will no one tell me what she sings?--
Perhaps the plaintive numbers flow
For old, unhappy, far-off things,
And battles long ago:
Or is it some more humble lay,
Familiar matter of to-day?
Some natural sorrow, loss, or pain,
That has been, and may be again?

Whate'er the theme, the Maiden sang
As if her song could have no ending;
I saw her singing at her work,
And o'er the sickle bending;--
I listened, motionless and still;
And, as I mounted up the hill,
The music in my heart I bore,
Long after it was heard no more.

A.
The poem is strongly nationalistic.
B.
The poem argues that high aspirations are good.
C.
The poem focuses on mysticism and the supernatural.
D.
The poem explores the inner world of an individual.