单选题What could be the reason for this（）AThe listener is not running on the database node.BThe TNS_ADMIN environmental variable is set to a wrong value.CThe orcl.oracle.com database service is not registered with the listener.DThe DEFAULT_DOMAIN parameter i
题目
单选题
What could be the reason for this（）
A
The listener is not running on the database node.
B
The TNS_ADMIN environmental variable is set to a wrong value.
C
The orcl.oracle.com database service is not registered with the listener.
D
The DEFAULT_DOMAIN parameter is set to a wrong value in the sqlnet.ora file.