奥斯特实验说明了____;通电螺线管附近小磁针如图所示,则电源的a端是____极(选填“正”或“负”).
下列计算中,正确的有( )①am×an=amn;②am+n2=a2m+n;③2anb3×-16abn-1=-13an+1bn+2;④a6÷a3=a2。
— Were there any cows?
— ________.
下列对空气的描述不正确的是( )
I know a place __ we can have a big meal.