牙尖是()
A.牙冠上两个面相交形成
B.牙冠上三个面相交形成
C.牙冠上四个面相交形成
D.牙冠上五个面相交形成
E.牙冠上六个面相交形成
参考答案:C
-Hi, I didn't know you had come back! Have you finished your teaching in America?
-Yes. I______Chinese there for more than two years.
A.have been teaching
B.was teaching
C.taught
D.had taught
消费与储蓄的生命周期的含义是:工作期进行储蓄,退休期则使用过去的储蓄。()