____________ is very easy.
A:Make a card
B:Making a card
C:Makes a card
①BM与ED平行;
②CN与BE是异面直线;
③CN与BM成60°角;
④DM与BN垂直.
以上四个命题中,正确命题的序号是( )
若m·23=26,则m等于( )
粗盐提纯过程中,不需要用玻璃棒的步骤是( )