—Is this his dictionary?                                         

—Yes,_____ _____.                                                                                                                           [ ] 

A. it am                                                            

B. it is                                                            

C. it isn't                                                        

D. it's   

下列与观测线有关的叙述错误的是（）

A.观测线又称为导线

B.观测线以上的部分为基牙的非倒凹区

C.观测器的分析杆代表义齿的就位方向

D.观测线就是牙冠的解剖外形高点线

E.同一基牙由于就位道设计不同，观测线也就不同