Write a multi-choice question for the following article, with the given choices and answer: Article: What is time? Is it a thing to be saved or spent or wasted, like money? Or is it something we have no control over, like the weather? Is time the same all over the world? That's an easy question, you say. Wherever you go, a minute is 60 seconds, an hour is 60 minutes, a day is 24 hours, and so forth. Well, maybe. But in America, time is more than that. Americans see time as a valuable resource. Maybe that's why they are fond of the expression, "Time is money." To Americans, punctuality is a way of showing respect for other people's time. Being more than 10 minutes late to an appointment usually calls for an apology, and maybe an explanation. People who are running late often call ahead to let others know of the delay. Of course, the less formal the situation, the less important it is to be exactly on time. At informal get-togethers, for example, people often arrive as much as 30 minutes past the appointed time. But they usually don't try that at work. American lifestyles show how much people respect the time of others. When people plan an event, they often set the time days or weeks in advance. Once the time is fixed, it takes almost an emergency to change it. If people want to come to your house for a friendly visit, they will usually call first to make sure it is suitable. Only very close friends will just "drop by" unannounced. Also, people hesitate to call others late at night for fear they might be in bed. The time may vary, but most folks think twice about calling after 10:00 p.m. Options: A that Americans value punctuality B that in the USA time is limited and valuable. C the Americans attitude towards time. D the Americans' control over time. Answer: C the Americans attitude towards time. Question:
The main idea of the passage is _ .