已知向量a→=3,4,b→=sinα,cosα且 a→// b→,则tanα=( )
酗酒危害人体健康,实验人员以水蚤作为实验材料,在探究不同浓度的酒精对心率影响的实验中,必须人为改变的量(即自变量)是( )
Many people took hours ____(get) home yesterday because of the rainstorm.