A system of linear equation can have no solutions , many solutions or exactly one solution .
Let's check out example of each.
[tex]No \ Solution \\ x+y =2 \\ x+y=4[/tex]
[tex]Many \ solutions x+y =2 \\ 2x+2y=4[/tex][tex]Exactly \ one \ solution \\ x+y =2 \\ x-y=4[/tex]
So all of these describes a system of linear equations except two solutions.
So the correct option is B