In an Ex Post Facto Study Researchers ____________, and in an Experimental

In an ex post facto study researchers ____________, and in an experimental study researchers __________.

A) choose participants according to preexisting characteristics . . . . . manipulate conditions to produce differences
B) assign participants to groups randomly . . . . assign participants to groups according to some personal characteristics of participants
C) use more than one independent variable . . . . use one independent variable with two or more levels
D) conduct a survey . . . . conduct a correlation