题目内容：
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．water thread
B．assembly thread
C．water line
D．assembly line
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