which line is an example of iambic pentameter

The correct answer is C. And I do love thee: therefore, go with me
Explanation:
Iambic pentameter is a metric structure commonly used in poetry, especially traditional poems in English. This structure includes ten syllables in each verse and each pair of syllables is an iamb, which means, it includes an unstressed syllable and a stressed syllable, and therefore the iambic pentameter contains five (pentameter) iambs.
From the options presented, only option C is an example of iambic pentameter because this includes ten syllables (and/I/do/love/thee/there/fore/go/with/me), also each pair of syllables is an iamb, for example in "and I" "and" is unstressed and "I" is a stressed syllable.