Iambic pentameter is a line of verse in which stressed syllable is followed by an unstressed syllable. 'Penta' refers to five and 'meter' refers to measure. Therefore, it is foot or beat which have 10 syllables in each line or five iambs in each line.
For example, in Ode to Autumn by John Keats
“Close bosom-friend of the maturing sun;
Conspiring with him how to load and bless
With fruit the vines that round the thatch-eves run…
And fill all fruit with ripeness to the core;”
In the above-quoted lines, each line contains five iambs.
Therefore, the statement which correctly defines the structure of the iambic pentameter meter is a line of iambic pentameter contains five feet, with the stressed syllable following the unstressed syllable.
