The two girls _____ how to dance one month ago and now they can dance well.

诗歌鉴赏。
                                                                                               诉衷情     陆游     
                                                                                     当年万里觅封侯，匹马戍梁州。
                                                                                     关河梦断何处? 尘暗旧貂裘。
                                                                                     胡未灭，鬓先秋，泪空流。
                                                                                     此生谁料，心在天山，身老沧洲。

在冬奥会滑雪比赛时，运动员用力撑雪杖使自己从山上由静止加速滑下，这表明力能使物体的____发生改变；如图所示是某运动员在滑下过程中碰撞标志杆时的情景，它说明力还能使物体的____发生改变。