在没有世界贸易组织严格界定条件所列的例外情况下，一成员国不得歧视来自其他成员国的产品和提供者；同时，一成员国不得对合法入境的外国产品运用低于本国产品的歧视性待遇，这是“无歧视原则”的含义。( )

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．data

B．control

C．request

D．session