You buy food and clothes here.
A:It's the post office.
B:It's the supermarket.
实验是科学探究的重要方法,如图是测定空气中氧气含量实验的两套装置图,请结合图示回答有关问题.
(6-1.6)×0.25×2.3=____
构成一株油菜的结构层次依次是( )