Sometime too hot the eye of heaven shines

How many iambs are found in this line from "Sonnet 18"?

four

five

eight

ten

O

Five.

Explanation:

An iamb consists of two syllables, the first one of which is unstressed, and the second one which follows it is stressed. Additionally, all of Shakespeare's sonnets were written using iambic pentameter. A pentameter, consisting of the words penta (which means 5 in Greek) and meter (which refers to a duration of two syllables), consists of 10 syllables in total.

So, if there are ten syllables in one line, and an iamb consists of two syllables, that means that there are 5 iambs in total within one line in a Shakespearean sonnet.