If a classification, such that used to identify insects or rocks, is used in a scientific context, it is most often called a(n) ________ .

In experimental studies,

A) the investigator cannot make cause-and-effect inferences. B) investigators must take special precautions to control for participants' characteristics that could reduce the accuracy of their findings. C) the researcher directly controls or manipulates changes in the dependent variable. D) researchers gather information on participants without altering their experiences.

Of the following events in boys' puberty, which typically occurs earliest?

A) Growth of the genitals B) Peak of the growth spurt C) Growth of a beard D) Lowering of the voice