Attention, please! All the mobile phones ____ ____ ____ ____ before the meeting starts.
(____) They're on Shelf A.
(____) Well, let me help you.
(____) But I can't find the book.
(____) Where are the books about sports, please?
(____) Do you know the name of the book?
如下图所示,这个三角形的面积是2.8×3.2÷2=4.48( cm2 ).
能正确解释下列反应原理的离子方程式( )