Easy# Single Trajectory of an Autonomous Differential Equation

DIFFEQ-LCLYEA

Which of the following sets **CANNOT** represent a single trajectory of an autonomous differential equation ${\bf x}'={\bf f}({\bf x})$, where ${\bf f}:{\mathbb R}^2\rightarrow {\mathbb R}^2$ and ${\mathbb R}^2$ represents the plane?