Write a multi-choice question for the following article: Article: Now machines are widely used all over the world. Why are machines so important and necessary for us? Because they can help us to do things better and faster. A washing machine helps us to wash clothes fast. A printing machine helps us to print a lot of books, newspapers, magazines and many other things fast. Bikes, cars, trains and planes are all machines. They help us to travel faster than on foot. The computer is a wonderful machine. It was invented not long ago. It not only stores information but also stores numbers millions of times as fast as a scientist does. Let's study hard and try to use all kinds of machines to build China into a modern country.
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Question: Machines can help us to do things better and faster, so they _ .Options:A are difficult to makeB are expensiveC are important but not necessaryD are very helpfulAnswer:D