题目内容
The usual way to ensure reliable delivery is to provide the (16) 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 (17) frame bearing positive or negative (18) 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 frame to (19) 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, (20) hardware. （19）是（）
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简答题 简述植物密度效应的最后产量恒值法则，并解释最后产量恒值的原因。
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The purpose of the requirements definition phase is to produce a clear, complete, consistent, and testable (36) of the technical requirements for the software product.During the requirements definition phase, the requirements definition team uses an iterative process to expand a broad statement of the system requirements into a complete and detailed specification of each function that the software must perform and each (37) that it must meet. The starting point is usually a set of high-level requirements from the (38) that describe the project or problem.In either case, the requirements definition team formulates an overall concept for the system and then defines (39) showing how the system will be operated, publishes the system and operations concept document, and conducts a system concept review (SCR).Following the SCR, the team derives (40) requirements for the system from the high level requirements and the system and operations concept. Using structured or object-oriented analysis the team specifies the software functions and algorithms needed to satisfy each detailed requirement. （39）是（）
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