What do you ________ the villagers here?
A:think
B:thinks
C:think of
D:think over
40÷5=____
45÷9=____
6×9=____
7×2=____
72÷8=____
若e1→·e2→是夹角为60° 的两个单位向量,则a→=2e1→+e2→,b→=-3e1→+2e2→的夹角为( )