“The elegy written in a country churchyard” is written in:

The correct option is Quatrains of ten syllable lines.

Thomas Gray’s famous poem, "Elegy Written in a Country Churchyard," is composed using a specific poetic form known as elegiac stanzas or heroic quatrains.
A quatrain is a stanza containing exactly four lines. In this poem, each quatrain is written in iambic pentameter, which means each line contains five iambic feet, totaling ten syllables per line.
The rhyme scheme followed throughout the poem is abab, where the first line rhymes with the third, and the second line rhymes with the fourth.

Let's analyze the structural choices to understand why the other options are incorrect:
• Octava and sestet: This structure is characteristic of a Petrarchan (Italian) sonnet, which consists of an eight-line octave followed by a six-line sestet, totaling fourteen lines, rather than the continuous four-line stanzas of Gray's elegy.
• Heroic couplet: This form consists of rhyming pairs of iambic pentameter lines (aabbcc...), whereas the elegy uses alternating rhymes in four-line stanzas (quatrains).
• Alexandrines: An Alexandrine is a line of poetic meter that contains twelve syllables (typically iambic hexameter), which does not match the ten-syllable iambic pentameter lines used by Gray.