牙髓中发挥免疫功能的细胞是（）
A.成牙本质细胞
B.成纤维细胞
C.干细胞
D.成骨细胞
E.树突状细胞
参考答案：E
You can't imagine _______ when they received these nice Christmas presents. [ ]
A. how they were excited
B. how excited they were
C. how excited were they
D. they were how exited
技术相机的蛇腹我们又称之为（）。
A、托架
B、基座
C、皮腔
D、暗盒
E、皮老虎
F、对焦屏
