The EMP table has some discrepancy in data entry with a particular employee ID. You execute the
query as shown in the Exhibit to retrieve all versions of the row that exist between two SCNs.View the Exhibit.
Which two statements about the results of the query shown in the Exhibit are correct? (Choose two.)
Exhibit: 
A. The LAST_SCN value in the first row is NULL, which means that the versions of the row still exist at SCN 6636300.
B. The LAST_SCN value in the second row in NULL, which means that the version of the row still exists at SCN 6636300.
C. The LAST_SCN value in the third row is 6636280, which means that the version of row exists above SCN 6636280.
D. The LAST_SCN value in the second row is NULL, which means that the version of the row no longer exists because it was deleted.
此处 FIST_SCN 和 LAST_SCN 表明了行存在的一个时间点范围。第一行是最近的一个版本，其操作状态是 I 说明是 insert，LAST_SCN 是 null，在 6636298 之后的没有新版本，所以 A正确。
第二行的操作状态是 D 说明是 delete，也就是在 FIST_SCN 6636280 的时候删除了这个版本的行数据，所以此时 LAST_SCN 是 null，D 对。