May I have a pizza , please ?
403×91≈
21×198≈
369×9≈
354×38≈
397÷21≈
482÷79≈
811÷92≈
639÷82≈
Don't ____ ____ ____ the classroom.
下列应用及相应原理(用化学方程式表示)都正确的是( )