复数$\frac{2-i}{2+i}=$ (    )

在真空中有两个静止的点电荷，若保持它们之间的距离不变，仅将各自的电荷量均减小为原来的1/2，则它们之间的库仑力将变为原来的        (       )

    There're five members in my family—my parents , my grandparents, and me . My mother is a teacher. She teaches Chinese in our school. She likes music. My father is a teacher, too. He teaches art in the Guang Ming primary school. He likes going hiking. My grandmother is a worker. She likes reading books. My grandfather is a scientist. He likes playing chess. I am Betty. I'm in Shi Yan primary school. I like singing and dancing. Look! I have a happy big family. Isn't it?

下列生态系统中自动调节能力最强的是（  ）