18－9=（ ）
A： 3
B：6
C：8
D：9
____ (talk) with your parents often is a good way to make them understand you.
下列各项中与蛋白质作用无关的是（ ）
若方程组a+b=3b+c=2c+a=1的解满足k=a+b+c，求关于x的函数y=kx﹣k的解析式．
