Everyone hates to wait in lines. We get that anxious feeling that our precious life is slipping away while we're doing something so meaningless. But it's not always the length of the wait we find so unbearable. Some people camp outside Apple stores for an entire night just to get their hands on the latest product. But waiting 10 minutes in a grocery store just to buy a drink? Forget it. Our behavior when waiting is only partly decided by the length of the wait. "Often the psychology of queuing is more important than the statistics of the wait itself," notes the MIT researcher Richard Larson. One apparent aspect of queuing psychology is that we get bored when we wait in line. This issue is solved in many ways, from magazines in hospital waiting rooms to mirrors in elevators so that we can check our appearance. We really hate it when we expect a short wait and then get a long one. But studies show that we are much more patient when we are given an idea of how long we'll be waiting. Walt Disney Co knows this better than anyone else. It posts estimated waiting times for attractions in its theme parks. But according to Larson, these times are overestimated so that visitors get to the front of the queue more quickly than they expect. It keeps them happy. But perhaps the biggest influence on our feelings about waiting in a line has to do with our sense of fairness. When it comes to queues, the universally acknowledged standard is first come, first served. Any departure from this principle is regarded as unfair and can lead to violent queue anger. You've probably experienced mild queue anger yourself in fast food restaurants, watching people in the other line zoom ahead of you, cursing yourself for having chosen the "wrong" line. In order to solve this problem, the serpentine  line was invented. The serpentine line guides all customers into one big snaking queue, separated by ropes or barriers. When you reach the head of the queue, you are directed to the next available server, or teller, or customs official. The serpentine line isn't always faster than multi-lines before an array  of cash registers. But it offers important comfort: you absolutely never have to see someone arrive after you and get served before you. In life, waiting is inevitable. But a better understanding of the psychology of waiting can help make it a bit more bearable. When all else fails, bring a book or a smart phone will also do. The main purpose of the passage is   _  .
to explain the advantages of serpentine line to introduce ways of saving time in queuing to offer an explanation of the psychology of queuing to analyze the psychology of people queuing for Apple products