Sometimes the processes in which people are engaged are dependent upon other processes being completed first, possibly by other people. For example, on an automobile (71) , it is necessary for the body to be constructed before the doors can be added on. Attempting to add the doors first would be pointless, because there would be nowhere to attach them. Thus, if there is no body ready to have doors added, the process for adding doors has to be (72) until the process for creating the next body is complete. This is known as (73)
Obviously, there are many cases where people have to wait for other people to do something. However, if everyone in such a situation is waiting for someone else to do something first, then no one will ever be able to do anything. When discussing processes, this situation is known as (74) , because all of the involved processes are effectively dead because of locks they have on resources. Usually someone in such a situation will eventually notice and abort the process, allowing normal flow to (75) , and often warning signs can even be spotted ahead of time to avoid ’it in the first place.

A．suspended

B．broken

C．hung

D．hold

质量为5t的汽车在平直公路上匀速行驶。若车受到的阻力是车重的0.2倍。

（1）问这时汽车牵引力多大？

（2）如果牵引力增大，汽车的运动状况有何变化？

（3）如果汽车速度要减小，这时牵引力应怎样变化？