You connected to the database using the following connection string： CONNECT hr/hr@test.us.oracle.com：1521/mydb Which three statements are correct regarding the connection string？（）
A. mydb is a service name.
B. test.us.oracle.com is a database name.
C. 1521 is the listener port number.
D. mydb is a host name.
E. test.us.oracle.com is a net service name.
F. hr is a username.
G. test.us.oracle.com is an instance name.
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