Exhibit: 
View the Exhibit for some of the current parameter settings. A user logs in to the HR schema and issues the following commands:
SQL> CREATE TABLE emp (empno NUMBER(3), ename VARCHAR2(20), sal NUMBER(8,2)); SQL>
INSERT INTO emp(empno,ename) VALUES(1,'JAMES');
At this moment, a second user also logs in to the HR schema and issues the following command:
SQL> ALTER TABLE emp MODIFY sal NUMBER(10,2);
What happens in the above scenario?
A. The second user's session immediately produces the resource busy error.
B. The second user's command executes successfully.
C. The second user's session waits for a time period before producing the resource busy error.
D. A deadlock is created.
DDL锁等待时间参数时60，用户一最后一个insert DML未提交，用户二使用修改字段DDL语句，这时就要等待用户一DML提交，到了等待时间结束未用户一提交就会报资源繁忙。
DDL_LOCK_TIMEOUT specifies a time limit for how long DDL statements will wait in a DML lock queue. The default value of zero indicates a status of NOWAIT. The maximum value of 1,000,000 seconds will result in the DDL statement waiting forever to acquire a DML lock.
If a lock is not acquired before the timeout period expires, then an error is returned.