做空气中氧气含量测定的实验装置如图.下列有关说法正确的是( )
解方程组: {3a−b+c=72a+3b=−2a+b+c=−1
15____8+6
下列有关生物生殖和发育的说法,正确的是( )
— Mrs. White. She has lived in China for years. _____ Chinese is very good.