The major commercial species of Nicotiana that is grown for tobacco products is

In traditional cultures, gender-segregated play is a consequence of ____

a. differential brain development for boys and girls b. estrogen and testosterone within the bloodstream c. the X and Y chromosomes imposing on the child d. the gender-specific work of boys and girls

This threat to internal validity refers to problems in how groups were formed such that the

groups are not equal before the experiment. A) selection B) maturation C) testing D) history