**M**be a

*m*rows and

*n*columns matrix over GF(2). And Let

**M'**be a

*r*rows and

*n*columns submatrix of

**M**(

*r*<=

*m*). Note that rows of

**M'**is randomly selected from

**M**. Is it possible that the

**M**is full row-rank?

If it is, why?

If it is not, how about the case where

*r*<

*m*?