线圈abcd转动过程中经过图甲.乙位置时,导线a b所受磁场力的方向____(选填“相同”“相反”),原因是____.
系数化成整数且结果化为最简分式: 0.25a−0.2b0.1a+0.3b =____.
⑴ ____
⑵ ____
⑶ ____
⑷ ____
A. watching TV B. running C. jumping D. swimming