下列各句中，没有语病的一句是（） A．2009年3月28日所进行的“地球一小时”

急性根尖脓肿时，脓液最佳引流途径是

A．经龈沟引流

B．经牙周袋引流

C．经黏膜引流

D．经根管由龋洞引流

E．经牙槽骨由皮肤引流

自喷井分层采油主要是在油田开发（）采用的手段。

A、初期

B、中期

C、末期

D、高含水期

下列关于垂体瘤的描述中，不正确的是（）

A.垂体瘤90％为良性肿瘤

B.GH腺瘤如在青春期前发病者的主要表现为巨人症

C.如分泌生长激素过多可引起肢端肥大症

D.如一垂体瘤直径为12mm，应称之为微小腺瘤

E.如分泌催乳素过多可引起泌乳一闭经综合征和阳痿

在计算机外接设备中，UPS不间断电源属于（）

A.输入设备

B.存储设备

C.输出设备

D.保证计算机正常运转的电源保护设备

The usual way to ensure reliable delivery is to provide the (71) with some feedback about what is happening at the other end of the line. Typically, the protocol calls for the receiver to send back special (72) frame bearing positive or negative (73) about the incoming frames. If the sender receives a positive acknowledgement about a frame, it knows the the frame has arrived safely. On the other hand, a negative acknowledgement means that something has gone wrong, and the frame must be transmitted again.
An additional complication comes from the possibility that hardware troubles may cause a frame to (74) completely. In this case, the receiver will not react at all, since it has no any reason to react. It should be clear that a protocol in which the sender transmits a frame and then waits for an acknowledgement, positive or negative, will hang forever if a frame is ever lost due to, for example, (75) hardwareo

A．vanish

B．vary

C．appear

D．incline