The heroic couplet is a pair of

The correct option is: Ten-syllable lines that rhyme.

To understand why this is the correct choice, let us break down the components of a heroic couplet:
1. Couplet: In poetry, a couplet refers to a pair of successive lines of verse. Typically, these two lines share the same meter and are joined by a rhyme (ending with the same sound).
2. Heroic Meter: In English literature, the term "heroic" is traditionally associated with iambic pentameter, which is the standard meter used for epic, dramatic, and narrative poetry.

Let's look at the structure of iambic pentameter in terms of syllable count:
An iamb is a metrical foot consisting of one unstressed syllable followed by one stressed syllable (making 2 syllables per foot).
"Pentameter" means there are five of these metrical feet (iambs) in a single line.

Therefore, the total number of syllables in one line of iambic pentameter is:
$$5\times 2=10$$
This gives us exactly ten syllables per line.

Combining these definitions, a heroic couplet is a rhyming pair of lines written in iambic pentameter, meaning it consists of two rhyming, ten-syllable lines.