用a表示骨髓瘤细胞,表示已免疫的B淋巴细胞,则细胞融合过程中两次筛选的目的分别为 ( )
A:a、aa、ab、bb、b→a、aa、ab→ab培养
B:a、aa、ab、bb、b→ab、bb、b→ab培养
C:a、aa、ab、bb、b→ab→产生特定抗体的ab培养
D:a、aa、ab、bb、b→aa→能无限增殖的aa培养
缩句。
①广场上千万盏灯静静地照耀着天安门广场周围的宏伟建筑。
②残暴的敌人秘密地杀害了我们党的优秀领导人李大钊。
—__________.
“大包干,大包干,直来直去不转变,保证国家的,留足集体的,剩下的都是自己的”这首歌谣称赞的是( )
Danny's father is a firefighter. He works at fire station. He's very brave. He h____ short yellow hair. He is tall and thin. His c____ are orange. He likes putting out the f____. Danny's mother is a t____. She works in a school. Her students like her very much. She has a b____ and two dresses. They are purple.
They are nice. She likes playing games with her students. She is a good teacher.