Answer:
d) replication-plus-extension
Step-by-step explanation:
replication-plus-extension. a study in which researchers replicate their original study but add variables to test additional questions/participant variable. These extraneous variables are related to individual characteristics of each participant that may impact how he or she responds.
Since the first treatment was effective in decreasing social anxiety symptoms in adults who only had social anxiety
Also Dr. Reynolds knows people who have social anxiety disorder also often are depressed so he designed the second study to test the additional variable. hence D