儿童、青少年的骨具有很强的可塑性，其骨中的有机物主要是____ 。

用方框中所给词的适当形式填空，完成短文。

   Hello!  I’m Jenny. There ____  many festivals at our school. Let me____ you!  This month is October. All the ____  love October. In October, there is a Sports  Festival. We have a basketball game ____ a volleyball game during (在…期间) the festival. In the middle (中旬) of this month, we____  an English speech contest during the English Festival. October 19th is the day for a school trip. We go to Beijing ____  the teachers. On the last day of this month, there is a Music Festival. On that day, we can enjoy beautiful songs, piano music and so on. It is wonderful. Next month, there is ____ Art Festival. Students often display  (展示) ____  pictures on that day. I study and play games____  my school. It gives ____ happiness (快乐). I love my school very much.

如图所示，两个闭合圆形线圈A, B的圆心重合，放在同一个水平面内，线圈B中通如图所示的电流，设t=0时电流沿逆时针方向（图中箭头所示）．对于线圈A在t₁～t₂时间内的下列说法中正确的是

读“我国主要河流分布示意图”，完成下面小题：