先通读下面的短文，掌握其大意，然后从A、B、C、D四个选项中选择可以填入空白处的最佳答案。

    Edward has a pet dog and his name is Liston．Every day he1Liston for a walk in the park．He loves his dog very much．

    This morning，Edward has to go to the art club．So he goes to Liston and says．"I will come back2soon(很快)，Liston．Just stay in the garden and sleep3the tree．"And then Edward goes to the4station and gets on the bus．

    Liston doesn't want to 5Edward．He runs after Edward quietly．6the bus goes too tast,so Liston has to stop．

    After Edward comes home,he runs into the garden to7Liston and play with him．"Liston! Liston !8are you?"he shouts．But he can't see his dog．

    Edward walks up and down the street and calls dog's9．Then he hears(听到) Liston's bark(吠声)．"Liston!Liston!I'm here．" Liston runs to Edward10．Liston was waiting for him near the station．

硼化镁在39 K时呈超导性，可能是人类对超导认识的新里程碑。在硼化镁晶体的理想模型中，镁原子和硼原子是分层排布的，一层镁一层硼的相间排列，右图是该晶体微观空间中取出的部分原子沿Z轴方向的投影，白球是镁原子投影，黑球是硼原子投影，图中的硼原子和镁原子投影在同一平面上。确定硼化镁的化学式为 (    )

CH₃CH₂CH₂CH₃（正丁烷）和（CH₃）₂CHCH₃ （异丁烷）的关系是（　　）