A: You look very nice in your new dress today.B: Oh, really? I it when it was on sale.
A:buy
B:bought
C:have bought
D:will buy
下列化学方程式符合事实且书写正确的是( )
①实践是检验认识真理性的唯一标准 ②意识活动具有直接现实性
③量变达到一定程度必然引起质变 ④事物的发展是前进性和曲折性的统一