Read this quotation:
a horse! a horse! my kingdom for a horse!
-william shakespeare, king richard iii, act v, scene iv
why is this verse an example of iambic pentameter?

a. it contains five metrical feet, each with an unstressed and then a
stressed syllable.

b. the verse forms a pattern of an unstressed syllable immediately
followed by a stressed syllable.

c. it is a line from shakespeare, and his plays contain verse written
only in iambic pentameter.

d. the verse is 10 syllables long with an unstressed syllable at the
beginning and end.