△ABC的内角A，B，C的对边分别为a，b，c，已知b=3，三个内角A，B，C成等差数列．

若cosC=$\frac{\sqrt{6}}{3}$，求c；

地球由几大板块构成。一般说来，①____；而在外部，板块与板块之间的交界处，地壳不稳定。当大洋板块和大陆板块相撞时，大洋板块因密度大、位置低俯冲而下，往往形成海沟，成为海洋最深的地方；②____，隆起成岛弧和海岸山脉。太平洋西部的深海沟和岛弧链，就是太平洋板块与亚欧板块相撞形成的。在两个大陆板块相碰撞处，③____。世界最高峰喜马拉雅山就是印度板块和向亚欧板块碰撞过程中产生的。

下列对虫媒花说法错误的是（　　）

    No matter who will have difficulties at any time ，help is so necessary for everyone. The following1some advice on how to help the students who have trouble in studying.

    Help them set up the easier goal that they can achieve. The goal too high and the progress in a hurry only make us have trouble in studying. So in the daily lives and studying， they should achieve the learning goal step by step .After they make 2 progress ，they will go nearer to their last goal.

    Help them develop a good habit that is useful for 3learning .Good habits can improve grades. Before class ，they should prepare learning tools，4 markers， notebook， ruler， book etc. for the lesson. In the class ，they should listen to the teacher carefully and write down the notes. As the saying goes， “Excellence isn't 5 action， but a habit .”Good habits are the first step to success for the students who have trouble in studying.

    Help them overcome the inferiority(自卑) that is in their hearts. The students who have trouble in studying have strong inferiority more or less .So let them 6 confidence and believe their abilities. Let them believe their own strength and function .They need to tell themselves :“I can， I can study well，7 I work hard every class ，every day， every week and every term， the success will belong to me !”The person with enough 8 will be the strongest one on the earth.

    If you follow the advice above，you will help the ones who 9difficulties in studying . Without the sun， the moon isn't beautiful， either. Without the help from each other ，we also 10 warmth. Let's gives others who need help.