A：a
B：b
C：c
D：d
用化学用语填空．
①2个氮原子____；
②铁离子____；
③地壳中含量最多的元素____；
④氢氧化铝中铝元素显+3价____．
____
Liu Mei can speak Japanese so well! Who taught her?
Nobody. She taught _________.
