如图所示，轻弹簧一端固定，另一端自由伸长时恰好到达O点，将质量为m（视为质点）的物体P与弹簧连接，并将弹簧压缩到A由静止释放物体后，物体将沿水平面运动到B点．若物体与水平面的摩擦力不能忽略，则关于物体运动的下列说法中正确的是（   ）

①欢快活泼的泉水唱着歌儿奔向前方。____

②还有一些泉声忽高忽低，忽急忽缓，忽清忽浊，忽扬忽抑，是泉水正在绕过树根，拍打卵石，穿越草丛，流连花间……____

已知$\overrightarrow{a}=(2,1),\overrightarrow{b}=(-3,4)$则$\overrightarrow{a}$与$\overrightarrow{b}$的数量积为           （  ）

根据短文理解，从A、B、C、D四个选项中选择最佳答案。

    Almost everyone knows about Olympic Games. But not 1 people know how they started, why they once stopped and when the People's Republic of China took part in the Olympics.

    People 2 the first Olympic Games in Greece (希 腊）in 776 B. C. They had the Olympics 3 four years in summer. The first Olympics 4 for only one day and there was only one contest (比赛).It was a short race. Only Greek men could 5 in the race. Women couldn't 6 the race.

    When Rome (罗马）ruled Greece, the Olympics 7.

    The People's Republic of China took part in the Olympics 8 the first time in 1952. 9 China got no gold medals until (直到）1984 in the Los Angeles Olympics. China won the first 10 in the 29th Beijing Olympics in 2008. We hope China will get more gold medals in the 30th Olympics in London. Come on, the Chinese players!

酶是蛋白质因而具有蛋白质的特性，酶能催化许多有机化学反应。下图表示温度T(℃)与反应速度v关系的各曲线，有酶参加的是    (  )。