分泌胆汁的消化器官是( )
A:胆囊
B:肝脏
C:胰
D:唾液腺
My new classmates
I have two new classmates. They are Paul and Mary.……
已知直线ax+by+c=0与圆:x2+y2=1相交于A、B两点,且 |AB→|=3,则OA→·OB→=____ .