下列实验或实例,能用来探究声音的产生与传播:
已知a→,b→是平面向量,若a→⊥(a→-2b→),b→⊥(b→-2a→),则a→与b→的夹角是( )
读潜水位等值线图,右图表示甲图中XY两地间的剖面图。读图回答下列各题。
—Jenny, do you want to be a doctor in the future?
—No, my mom expects me a doctor but I want to he a teacher.