Final answer:
Police records and diaries have been used in studies on drug and gang subcultures.
Step-by-step explanation:
A) Police records
B) Diaries
C) Financial statements
D) Medical records
Police records are the type of records kept by subjects that are commonly used in studies on drug and gang subcultures. These records provide valuable information about criminal activities, arrests, and other relevant data. Diaries can also be used to gain insights into the thoughts and experiences of individuals involved in these subcultures. However, financial statements and medical records are not typically the types of records used in these studies.