在switch（expression）语句中，expression的数据类型不能是（）。

A、double

B、char

C、byte

D、short

Which of the following is a secure method of remote access via command line?（）

A、RCP

B、Telnet

C、RSH

D、SSH

Which of the following devices transmits timed broadcasts onto an active network?（）

A、Bridge

B、Unmanaged switch

C、DHCP client

D、Firewal

Which command will create a group called ’delivery’ and set the administrators to ’john’ and ’mary’？（）  

A、mkgroup -A=john，mary delivery

B、groupadd -A=john，mary delivery

C、mkgroup adms=john，mary delivery

D、groupadd adms=john，mary delivery

Which node type will use only NetBIOS broadcast requests using UDP broadcast？（）

A、 b-node （type 0x01）

B、 p-node （type 0x02）

C、 m-node （type 0x04）

D、 h-node （type 0x08）

You execute the following Recovery Manager （RMAN） commands in he following order：   BACKUP VALIDATE DATABAE RECOVER CORRUPTION LIST；   Which two tasks are performed by these commands？（）  

 Repair the corrupted blocks. If any. In the backup created

 Populate VSCOPV_CORRUPTION with names of files that have corrupted blocks

 Back up the database after checking whether array of the files have corrupted blocks

 Discover any corrupt blocks that are viewable with the VSDATABASE_BI-OCK_CORBUPTION view

 Repair all corrupted blocks that have been logged in the VSDATABASE_BLOCK_ CORRUPTION