将长为1 m的导线ac从中点b折成如图所示的形状，放入B＝0.08 T的匀强磁场中，abc平面与磁场垂直．若在导线abc中通入25 A的直流电，则整个导线所受安培力大小为

____ N.

元朝赵天麟说：“今立行省于外，维持错综，众建其官，有诸侯之镇而无诸侯之权，可谓于审力之形矣。”材料体现了元代行省制的哪一特点？

完形填空
      It's a fine Sunday morning. The weather is1. A lot of children2 in the park. They are3 happily. Some are playing4 under a big tree. Some girls are singing and dancing. Some boys are running5 the hill. Li Lei is6by the lake. He's reading a story. 7 is Wang Lin? He's standing over there. 8is he doing? He's looking9 a nice butterfly（蝴蝶）. He10to catch (捉住) it. 

$\sqrt{16}$的平方根是（   ）