如果用Begg矫治器治疗，颌间牵引的力应是
A．60g左右B．150g左右C．300g左右D．200g左右E．250g左右
参考答案：A
Tom sat under a tree chatting with his friends and _____ his teacher, stood up in no time.
A．seeing
B．seen
C．saw
D．to see
函数f（x）=ax+b有一个零点是2，那么函数g（x）=bx2-ax的零点是______．
