A researcher is interested in the effects of a preschool program on later school performance. Because she is concerned that socio-economic-status (SES) is a potential extraneous variable in her study, she picks^&tyldren to study who are only from low SES homes. The control technique she used in this study was- ----

• A. Matching
• B. Random assignment
• C. Holding the extraneous variable constant
• D. Statistically controlling the extraneous variable