It's important_______ the piano well.
A:of him to play
B:for him to play
C:of him playing
D:for him playing
①将固体溶于水得无色透明溶液,加入足量BaCl2溶液,过滤后得到5克白色沉淀。
②在沉淀中加入过量稀硝酸,仍有3克白色沉淀。
③在滤液中滴加AgNO3溶液,产生白色沉淀。则该固体中一定含有( )
看图回答
有理数a、b在数轴上的位置如图所示,则下列各式错误的是( )