If the population of a certain country increases at the rate of one person every 20 seconds, by how many persons does the population increase in 30 minutes? Choose the correct choice from the following choices:
A) 55  B) 20  C) 96  D) 90  E) 40
Answer = 3 * 30= 
<gadget id="calculator">3 * 30</gadget>
<output>90</output>
90   Answer= 90
<result>D</result>
If the population of a certain country increases at the rate of one person every 20 seconds, by how many persons does the population increase in 30 minutes?