Wordsworth’s "Tintern Abbey" is written in blank verse, which means:
Unrhymed lines
Written in iambic pentameter (five metrical feet per line, each foot with an unstressed-stressed pattern)
So while iambic pentameter (option b) describes the meter, blank verse (option c) is the correct term for the overall style, since it refers specifically to unrhymed iambic pentameter — the form Wordsworth uses in this poem.