$\displaystyle{\stackrel{{\leftrightarrow}}{{{P}{Q}}}}{\mid}{\mid}{\stackrel{{\leftrightarrow}}{{{R}{S}}}}\usepackage{cmbright}\Huge\$ , $\displaystyle{\stackrel{{\leftrightarrow}}{{{P}{Q}}}}{\mid}{\mid}{\stackrel{{\leftrightarrow}}{{{T}{U}}}}\usepackage{cmbright}\Huge\$ , and $\displaystyle{\stackrel{{\leftrightarrow}}{{{R}{S}}}}{\mid}{\mid}{\stackrel{{\leftrightarrow}}{{{T}{U}}}}.\usepackage{cmbright}\Huge\$ So there are three pairs of parallel lines.