问题
选择题
— Do you often practice ______ English with your classmates after class?
— Yes, and it improves my speaking skills.
A．to speak
B．speaking
C．to say
D．saying
答案
答案：B
说某种语言用speak，practice接动名词表示反复做，接不定式表示目的。所以选B。
上下牙槽骨的吸收变化是（）