For what value of a and b will the following system of linear equations have infinitely many solution? $2x - (a-4)y=2b+1;4x-(a-1)y =5b-1$

Question

$(A) \; a=6;b=3 \\(B)\;a=8;b=4 \\(C)\; a=7;b=3 \\(D)\;a=9;b=4$