The teacher tells us that ______ careful we are, ______ mistakes we will make.
A:the more; the fewer
B:the fewer; the more
C:the more; the more
D:the less; the fewer
已知 {x=1y=2 是二元一次方程组 {3x+2y=mnx−y=1 的解,则m﹣n的值是____.
下面做法中值得提倡的有( )