Hi does anyone know how to do this question? im unsure about the theory as well.thanks.

If A is a 7x5 matrix with reduced row echelon form R and B is a 4x6 matrix with reduced row echelon form S. Which of the following statements are always true.

R has at least one zero row/ S has at least one zero row/R has at least one column without a leading one /S has at least one column without a leading one /The system Ax=b has at least one solution for all b which is an element of R^{7}/The system Bx=0 has infinitely many solutions .