—_________ weather it is! We can't go boating on the Xuanwu Lake.
—Don't worry. Let's go to the Science Museum instead.
A：What good
B：How good
C：How had
D：What bad
对于任意自然数Χ、y，规定f（Χ）=2Χ﹣1，g（y）=y÷2+1，则f（10）﹣g（10）=（ ）
生物的遗传和变异是通过____和____而实现的．
