If a student asks you why we can see colors and you want to provide an answer based on the opponent-process theory of color vision, you tell the student it is because there are different types of cone receptors.

four                  

Explanation:

The answer is there are "four" different types of cone receptors.

          The concept of opponent process theory is first given by Ewald Hering. According to his theory, people can never see certain combination of colors.

           According to Hering's opponent-process theory of color vision, the ability to see colors is controlled by the receptor complexes that has opposing actions. They are the blue-yellow complex, red-green complex and black-white complex.

         The cells opposes the two color and we are able to see only one color at on  time. For example, we are able to see or perceive either red color or the color green at one time.

          We have four different cone cells or cone receptors in our eye and the condition of having four different cone receptors or or channels to perceive colors is called 'tetrachromacy'.

Therefore the answer is -

"four"

i thought a 14 year old should know this but

colonies   were tied to britain through trade and by the way they were governed.   trade was restricted so the colonies had to rely on britain for imported goods and supplies.   there were no banks and very little money, so colonists used barter and credit to get the things they needed.  

britain also needed money to pay for its war debts.   the king and parliament believed they had the right to tax the colonies.   they decided to require several kinds of taxes from the colonists to pay for the french and indian war.   these taxes included the stamp act, passed in 1765, which required the use of special paper bearing an embossed tax stamp for all legal documents.   other laws, such as the townsend acts, passed in 1767

this mainly outraged the colonies and created what we know as today as the american revolutionary war

the answer to your question is,

d. when a child was born.

-mabel < 3