C
you don't need to know how I know.
In iambic pentameter, each verse consists of five metrical feet. Meter is a poem's rhythm, and feet are units of that rhythm.
In an iamb, an unstressed syllable is followed by a stressed syllable, as in the word "hello."
"Penta" means five, so a verse of iambic pentameter has five iambs.
Five pairs of unstressed syllables followed by stressed syllables.
Five pairs gives a total of ten syllables. So the answer is B, "each line contains ten syllables."
