Answer:
“He only says, ‘Good fences make good neighbours.’”
Explanation:
Blank verse is a style of poetry in un-rhyming verses written in iambic pentameter. That is, it has ten syllables in each line, with a stressed syllable following an unstressed syllable but the five stressed syllables are not rhymed.
Among the given lines from the poem "Mending Wall" by Robert Frost, the line that contains an irregular line of blank verse is <u><em>"He only says. 'Good fences make good neighbors.'" </em></u>This line contains not 10 syllables but 11, unlike the other lines which are all in pentameter form. The other lines in the options all have ten syllables each. Thus, this irregularity makes it the odd one out.
Therefore, the correct answer is the first option.