世界各国自然条件差异巨大，经济发展水平极不平衡，根据所学世界地理知识，有“石油王国”之称的是（  ）

如图1所示，在弹簧测力计下挂一圆柱体，从盛水的烧杯上方某一高度缓慢下降，圆柱体浸没后继续下降，直到圆柱体底面与烧杯底部接触为止，如图2所示是圆柱体下降过程中弹簧测力计读数F随圆柱体下降高度h变化的图象．根据题目条件,试求下列问题：

根据材料内容，选择正确答案。

    Toronto is the biggest city in Canada. It is famous for the CN tower, Niagara Falls(尼亚加拉大瀑布)and some other famous places.

    The CN tower is 553 metres high. It is the world's highest tower. You can stand on a glass floor. Do you think it may break? If you think so, you are wrong, because the glass is very strong. If you look down from the CN tower, you will see a large stadium, the Skydome (天虹体育馆). The Skydome has a special(特殊的) roof(屋顶). The roof can open and close. So don't worry about the rain when you are watching a match there.

    Niagara Falls is one of the biggest falls in the world. It is made up of two falls. One is in the US. People call it American Falls. The other is in Canada. People call it Canadian Horseshoe Falls. The Horseshoe Falls drops from 52 metres high. It is 679 metres long. The sound of the water falling is so loud there. You cannot hear yourself talk! It is very exciting!