A:a; the
B:a; 不填
C:a; a
D:不填; 不填
人们常说“作茧自缚”,说的是蚕发育过程的哪个时期( )
稀有气体元素的原子,最外层电子数可能是( )
①8 ②3 ③4 ④2.
—Yes, you can. But you must know how to _________ it.