One day, in an English class, the students are having their lessons. Their teacher, a young woman is very happy. She sings some nice songs with them and then she goes to the blackboard and writes “SMILES” on it. “This is the longest（最长）word in English,” she says to the class.
   A girl stands up and says, “It has only six letters. How can it be the longest word in English?”The teacher smiles and says, “Oh, look! There is a mile（英里）between the first letter and the last one.”

下列大洲中，所包含的发达国家个数最多的是（　　）

把质量相等的A、B两物体挂在图所示的滑轮组下而，不计绳子、滑轮的重力和摩擦，放手后(    )

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