Even though you didn't give as the verse or your options, this question can still be answered nevertheless by explaining what an iambic pentameter is.
The first part of the phrase, iambic, refers to a type of a metrical foot known as iamb. It refers to the sequence of two stressed and unstressed syllables, the first one being unstressed.
The second part of the phrase, pentameter, refers to the meter of that particular line in a poem. One meter contains two syllables, and the word penta comes from Greek and means five. So if you multiply the two, pentameter is a line consisting of 10 syllables.
So, an iambic pentameter is a line of 10 syllables where the first one is unstressed, and the one that follows it is stressed.
Here is an example:
Shall I compare thee to a summer's day?
(Shakespeare often wrote in iambic pentameter)