下列纬线圈中长度最长的是( )
A:15°N
B:20°S
C:25°N
D:30°S
求几个加数的和,用乘法计算比较简便.
— is it from your home to the railway station?
—It is about twenty minutes by bus.
如图,从边长为(a+4)cm的正方形纸片中剪去一个边长为(a+1)cm的正方形(a>0),剩余部分沿虚线又剪拼成一个矩形(不重叠无缝隙),则矩形的面积为( ).