Part a which lines from the poem best shape the theme that joy can be found in experiencing the natural world? "for oft when on my couch i lie / in vacant or in pensive mood," "they stretched in never-ending line / along the margin of a bay: " "beside the lake, beneath the trees, / fluttering and dancing in the breeze." "a poet could not but be gay / in such a jocund company: "

The lines in the poem that best shape the theme that joy can be found in experiencing the natural world are:  "Beside the Lake, beneath the trees, /Flittering and dancing in the breeze."  "A poet could not but be gay/ In such a jocund company".  The first lines "Beside the Lake..." depict a natural scenery and the lines that follow: "A poet could not but be gay...", express that the company of nature makes a poet very happy and feel in good company.  The theme is expressed clearly in this set of lines.    

These lines are from the poem I Wandered Lonely as a Cloud  also known as The Daffodils, by the great English Romantic poet William Wordsworth.

The lines from the poem which best show that joy can be found in experiencing the natural world are:

         Fluttering and dancing in the breeze."

He was inspired to write this poem on one of the many walks he took with his sister (Dorothy) in the Lake District. He uses personification to describe the joy these daffodils must feel while they 'dance in the breeze'.