Ambic pentameter is a meter with
a. four unstressed and stressed syllables in a row.
b. five unstressed and stressed syllables in a row.
c. four stressed and unstressed syllables in a row.
d. five stressed and unstressed syllables in a row.

Iambic pentameter is a meter with five unstressed and stressed syllables in a row. Since it says pentameter, it means there are 5 meters, and since 1 meter consists of 2 syllables, that means that one line consists of 10 syllables, which go: unstressed, stressed, unstressed, stressed, etc. until you reach the 10th one.
For example: 
When I do count the clock that tells the time, 
To swell the gourd, and plump the hazel shells. 

YEET CNA YOU SYA THAT PLZ

Explanation: