Which of the following statements about the secondary use of personal information is correct?
A、Secondary use is the use of personal information for a purpose other than the one for which the person supplied it.
B、Transfer the personal information provided by the user at the time of registration to other companies. This is a kind of secondary use.
C、The common technologies involved in the secondary use of personal information include data mining and user characteristics analysis etc.
D、The second use of user's personal information on the network platform is completely unnecessary for users to know.