Do you love the holidays, but hate gaining weight? You are not alone. Holidays are times for celebrating. Many people are worried about their weight. With proper planning, though, it is possible to keep normal weight during the holidays. The idea is to enjoy the holidays but not to eat too much. You don’t have to turn away from the foods that you enjoy.
| D．Physical exercise can reduce the chance of putting on weight. | B．Creamy food. |
| D．Wonderful holidays, boring weight. |
，则f（x）= ．
如图所示，长为L、内壁光滑的直管与水平地面成30°角固定放置．将一质量为m的小球固定在管底，用一轻质光滑细线将小球与质量为M=km的小物块相连，小物块悬挂于管口．现将小球释放，一段时间后，小物块落地静止不动，小球继续向上运动，通过管口的转向装置后做平抛运动，小球在转向过程中速率不变．（重力加速度为g）
L．
