—Oh, sorry. But what did you say just now? I _______ something else.
A:thought
B:was thinking
C:am thinking
D:will think
①在国民经济中居于主导地位
②与社会化大生产紧密联系
③在社会总资产中占优势
④在国民经济中处于主体地位
下列操作中,能鉴别空气、氧气和氢气3瓶气体的是