科学工作者为了探测海底某处的深度，向海底垂直发射，经过3.8 s收到回声信号，海

鳍是鱼类的运动器官，并起着重要的协调作用，尾鳍的作用是（　　）

A．保持鱼的身体平衡

B．感知水流的变化

C．保持鱼体前进的方向

D．减少水流的阻力

排便时由于肛裂内_______受刺激，立即感到肛门________样或_______样疼痛。

天气寒冷时，点火时间应稍为推迟，炎热时适当提前。

淖浦噶举派的淖浦译师曾延请了哪三 位印度班智达？

Electronic mail, or mail, as it is known to its many fans, has been around for over two decades. Typically, email systems support five basic functions, as described below. (41) refers to the process of creating messages and answers. (42) refers to moving messages from the originator to the recipient. (43) has to do with telling the originator what happened to the message. Was it rejected Was it lost (44) incoming message is needed. So people can read their email. (45) is the final step and concerns what the recipient does with the message after receiving it.

A．Composition

B．Terminating

C．Reporting

D．Displaying