There are many old people _______ are taking a walk in the park.
A:those
B:which
C:who
D:whom
今天小华做了5道语文题,6道数学题,还有7道英语题,小华今天一共做了18道题.
基因型为BB的个体占18%、Bb的个体占78%,基因B和b的基因频率分别是( )