Final answer:
The motive behind supernatural elements in Romantic poetry is to promote religious orthodoxy.
Step-by-step explanation:
The motive behind supernatural elements in Romantic poetry is c) To promote religious orthodoxy.
The Romantic poets, such as William Wordsworth and Samuel Taylor Coleridge, were known for their exploration of the irrational and mysterious (a), their challenge to conventional beliefs (b), and their desire to evoke strong emotions in readers (d).