What is true for a typical two$-$dimensional flow $($x$-$y plane$)$ over an airfoil?

Question $2$ options:

a$)$

Two streamlines define the flow in the x$-$y plane and z$-$axis.

b$)$

Two streamlines define the flow in the x$-$y plane and x$-$axis.

c$)$

Two streamlines define the flow in the x$-$y plane and y$-$axis.

d$)$

Only one streamline defines the flow in the x$-$y plane.