What is iambic pentameter?
a. a metrical foot consisting of a stressed syllable followed by an unstressed syllable
b. a unit of spoken language made up of an uninterrupted sound, most often consisting of a vowel and one or more consonants
c. two or more words or syllables that have a similar or identical sound within a poem or line of verse
d. a line of verse with 10 alternating unstressed and stressed syllables

An "iamb" is a unit of speech or poetry that's made of
one unstressed syllable plus a stressed syllable after it.

Examples:

" new YORK "

" ma DRID "

" that's IT ! "

" hel LO "

"Penta..." means "five", like in a "pentagon".

"Pentameter" means a line of speech or poetry that has five units in it, no matter what
their form is.

"Iambic pentameter" is a line of speech or poetry that has five 'iambs' in it.

Example: 

" to BE  or NOT  to BE  that IS  the QUES "                                     (chun)

The lyrics (words) to the 'blues' are almost all Iambic Pentameter
or close to it:

__ See  that SPI  der CRAWL  in' UP  that WALL

If you SEE    me COM   in', HEIST  your WIN   dow HIGH .
If you SEE    me COM   in', HEIST  your WIN   dow HIGH .  
If you SEE    me GO  in', baby, HANG   your HEAD   and CRY.

It's been THREE  weeks SINCE  my sweet BA  by SAID  goodBYE .
It's been THREE  weeks SINCE  my sweet BA  by SAID  goodBYE .
And NOW    my sweet DOG    has EAT  en ALL OF  my sweet PIE . 

The correct choice is 'd' .

Two because two of one thing is two.