A plane flow has velocity components $u=\dfrac{x}{T_1}$, $v=-\dfrac{y}{T_2}$ and $w=0$ along $x,y$ and $z$ directions respectively, where $T_1( \neq 0)$ and $T_2 (\neq 0)$ are constants having the dimension of time. The given flow is incompressible if

1. $T_1=-T_2 \\$
2. $T_1=- \dfrac{T_2}{2} \\$
3. $T_1=\dfrac{T_2}{2} \\$
4. $T_1=T_2$