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) flame bearing positive or negative (73) about the incoming frames. If the sender receives a positive acknowledgement about a frame, it knows 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 flame 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) hardware.

（74）处应填（）。

A．vanish

B．vary

C．appear

D．incline

“通过加强随访和管理，提高个人和家庭自我保健能力，预防进一步恶化”，这一高血压病社区健康教育对策主要适用于（）。

A.高危人群

B.青少年

C.高血压患者

D.社区群众

E.社区领导