小明同学所做的下列家庭小实验中，主要发生物理变化的是(    )

1千克面粉可磨面粉0.8千克，50千克小麦可磨面粉____千克。

诗歌欣赏。
                                                                                                   移家别湖上亭  
                                                                                                       戎昱
                                                                                    好是春风湖上亭，柳条藤蔓系离情。
                                                                                    黄莺久住浑相识，欲别频啼四五声。