The Young-Helmholtz theory of color vision postulates ( ) receptors, whereas the Hering opponent-process theory of color vision postulates ( ) receptors.

It is probable that up to 4 billion children born between the years 1950 and 2008 would have died without the institution of public health practices

Indicate whether this statement is true or false.

At the end of the 20th century, about _____ American teens graduated from high school

A) half of B) two-thirds of C) three quarters of D) nine in ten