You work in a company which is named Wiikigo Corp. The company uses SQL Server 2008. You are the administrator of the company database. Now you are in charge of a SQL Server 2008 instance. There is a database named DB1 in the instance. You have set the recovery model of DB1 to Full. At 2：00 There is a full database backup of all the user databases every day. Every quarter the transaction log backup is performed. Every 4 hours a differential backup is occurred. You are going to perform a full backup of DB1 at 11：00. When you perform this back up， you must make sure that the overall backup will not be affected. What'；s more， you have to restore procedures for DB1. You must make sure that the backup files are restored in proper sequence. 
In the options below， which Transact-SQL statement should you use？（）

A.BACKUP LOG DB1 TO DISK = 't:\backups\db1.trn'; 
B.BACKUP DATABASE DB1 TO DISK = 't:\backups\db1.bak' WITH DIFFERENTIAL; 
C.BACKUP DATABASE DB1 TO DISK = 't:\backups\db1.bak' WITH NOUNLOAD; 
D.BACKUP DATABASE DB1 TO DISK = 't:\backups\db1.bak' WITH COPY_ONLY;