①北半球比南半球陆地多 ②南半球比北半球陆地多

③东半球比西半球陆地多 ④西半球比东半 球陆地多

用所给词的适当形式填空

①—Where is Mr. Green?

—He ____ (go) to Beijing on business.

②You mustn't swim in the lake. Look at the sign “No ____ (swim). ”

③ After school, he always finishes ____ (do) his homework first.

④ My sister ____ (arrive) at the airport in two hours.

⑤ David is coming to visit us. I’m looking forward to ____ (meet) him.

如图所示，由不同物质制成的甲、乙两种实心球的体积相等，此时天平平衡．则制成甲、乙两种球的物质密度之比为（　　）

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如果直线a∥b，b∥c，那么直线a与c的位置关系是____