生物膜成熟的标志有哪些？
参考答案：生物沿水流的分布，生物膜上由细菌及各种微生物组成的生态系统，对有机物的降解功能都达到平衡和稳定状态。
A．人耳听不见的超声波和次声波，但有的动物却能听见
B．足够强的超声波才能被人听见
C．次声波对人体有百害而无一利
D．人耳听不见的声音都叫超声波
In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.
In low-speed network, it is usually adequate to wait for congestion to occur and then react to it by telling the source of packets to slow down. In high-speed networks, this approach often works poorly, because in the (71) between sending the notification and notification arriving at the source, thousands of additional (72) may arrive. In ATM network, a major tool for preventing (73) is (74) control. When a host wants a new virtual (75) , it must describe the traffic to be offered and the service expected.
72（）
A．packets
B．cells
C．message
D．files
