题目

Jim has made many friends since he ______ to China.A．cameB．comesC．has comeD．will come 答案：A解析:略根据达尔文进化学说当今丰富多彩的生物界形成的原因是 A．生存斗争     B．自然选择     C．人工选择     D．遗传变异