For a two-dimensional, incompressible flow having velocity components $u$ and $v$ in the $x$ and $y$ directions, respectively, the expression

$$\frac{\partial \left ( u^{2} \right )}{\partial x}+\frac{\partial \left ( uv \right )}{\partial y}$$

can be simplified to

1. $u\frac{\partial u}{\partial x}+u\frac{\partial v}{\partial y}$
1. $2u\frac{\partial u}{\partial x}+u\frac{\partial v}{\partial y}$
1. $2u\frac{\partial u}{\partial x}+v\frac{\partial u}{\partial y}$
1. $u\frac{\partial u}{\partial x}+v\frac{\partial u}{\partial y}$