经测定某中性溶液中含有Mg2+、Al3+、NO3﹣、SO42﹣四种离子组成,其中Mg2+、Al3+、SO42﹣的个数比不可能为( )
如图是某几何体的三种视图,则该几何体是( )
He has ________ in touch with his foreign friends for many years.