【简答题】看图完成句子。 1. There ______________________ under the umbrella. 2. There ______________________ on the desk. 3. There ______________________ behind the door. 4. There ______________________ on the shelf.
【单选题】渐缩喷管工作在初压p1和极低背压pb之间,初速略去不及,若喷管出口部分切去一小段,则工质的出口流速_____,流量_______。
【单选题】工作在恒定初压p1和极低背压pb之间的渐缩喷管,在出口截去一小段后,其出口流速: 。
【简答题】Under negotiation credit, the negotiating bank make payment to the beneficiary (1)( ) with recourse. (2)( ) without recourse.