A:where Maria had put
B:where had Maria put
C:where has Maria put
D:where Maria has put
假定五对等位基因自由组合,则杂交组合AaBBCcDDEe×AaBbCCddEe产生的子代中,有一对等位基因杂合、四对等位基因纯合的个体所占的比率是( )
以下做法有利于保护生物圈的是