A:①②③
B:①②④
C:②③④
D:①③④
32×5+35×8+38×11+…+31991×1994+31994×1997=____ .
It's a nice day. What about in the park?
已知不共线向量a→,b→,a→=2,b→=3,a→·b→-a→=1则b→-a→( )