若X为铜,为减缓铁的腐蚀,开关K应置于____ 处;若X为锌棒,开关K置于M处,该电化学防护法称为____
7个5是____.
____的4倍是20.
数据5,7,5,8,6,13,5的中位数是( )
Many people ________ their friends or family by mobile phone today.
既是正数又是分数,这样的数是什么数,举两例说明.