My family is ____(计划) a journey to China in the winter. Our first ____(选择) is to visit Beijing, one of the____(大) places in the world.. So we need to ____(预订) the plane tickets. To tell you the truth, we like going by train____ (好) . But we think it is too slow and it ____(花费) much time. Though going by plane is more____(昂贵的)，it goes____(快) and saves time. Some people may think it's not ____(安全) , but our family all____(赞同)it's our favorite way to travel.

甲、乙两同学骑自行车从A地沿同一条路到B地，已知乙比甲先出发，他们离出发地的距离s(km)和骑行时间t(h)之间的函数关系如图所示，给出下列说法：

(1)他们都骑行了20km；      
(2)乙在途中停留了0.5h；
(3)甲、乙两人同时到达目的地；
(4)相遇后，甲的速度小于乙的速度．
根据图象信息，以上说法正确的有（  　　 ）．

①关节面上有一层光滑的关节软骨

②关节囊为坚韧的结缔组织

③关节腔内有关节囊内壁分泌的滑液

④关节囊外有坚韧的韧带