读“欧洲西部图”，回答下列问题。

    Hello，my name is Danny. I am a tall boy. I have a big face and two big eyes. I can read books and write English. I am a good student. I have a happy family. My father and mother are teachers. My father is 35 years old and my mother is 33 years old. My father is tall and thin. He can swim and dive. My mother isn't tall. But she's thin. She can draw nice pictures.

步骤一：配制培养基：通常加入琼脂或明胶以便形成固体培养基．

步骤二：重复实验：A组实验接种正常R型细菌；B组接种正常S型菌；C组接种加热杀死的S 型菌：D组接种加热杀死的S型菌和正常的R型菌的混合液．培养结果如下．