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.