关于局域网交换机，下列表述错误的是( )。

A．直接交换方式不支持输入输出速率不同的端口间的帧转发

B．存储转发方式在转发前要进行差错检测

C．端口号/MAC地址映射表是通过“地址学习”来获得的

D．改进的直接交换方式在收到帧的前16个字节后判断帧头是否正确

Before a transesophageal echocardiogram, a client is given an oral topical anesthetic spray. Upon return from the procedure, the nurse observes that the client has no active gag reflex. In response, the nurse should（）

A. insert an oral airway.

B. withhold food and fluids.

C. position the client on his side.

D. introduce a nasogastric (NG) tube.