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.

（73）处应填（）。

A．application

B．connection

C．stream

D．acknowledgement

在19世纪中期以后的种种改革思想和实践的影响下，( )于1898年出版了以《明天：通往真正改革的平和之路》为书名的论著，提出了田园城市的理论。

A．索利亚
B．西谛
C．戈涅
D．霍华德