It seems that El Niño ____ some disasters in the world in the past few months.
A:has caused
B:is causing
C:will cause
D:caused
世界大多数农作物和动植物都能在我国找到适合生长的地区,是因为我国( )
请计算:
已知向量a→=x1,y1,b→=x2,y2,若|a→|=2,|b→|=3,a→·b→=-6,则x1+y1x2+y2的值为( )