—Jenny and Joe have________recently.
—How come?As far as I know,they have been good friends for many years.
A:picked up
B:made up
C:split up
D:given up
在Al2(SO4)3和MgSO4的混合溶液中,滴加NaOH溶液,生成沉淀的量与滴入NaOH溶液的体积关系如右图所示,则原混合液中Al2(SO4)3与MgSO4的物质的量浓度之比为 ( )
若平面向量a→=(1,2),b→=(﹣2,y)且,则a→⊥b→,则|b→|=( )