Which one of the following is a tridentate ligand

$\underset{¯}{{\mathrm{H}}_2\mathrm{N}}-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\underset{¯}{\mathrm{NH}}-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\underset{¯}{{\mathrm{NH}}_2}$ is diethylene triamine, a tridentate ligand ($\mathrm{dien}$). 

${\mathrm{H}}_2\mathrm{N}-{\left({\mathrm{CH}}_2\right)}_3-{\mathrm{NH}}_2 \mathrm{is} \mathrm{trimethylenediamine}\left(\mathrm{tn}\right) \mathrm{a} \mathrm{bidentate} \mathrm{ligand}.$

$\underset{¯}{{\mathrm{H}}_2\mathrm{N}}-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\underset{¯}{\mathrm{NH}}-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\underset{¯}{\mathrm{NH}}-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\underset{¯}{{\mathrm{NH}}_2}$ is triethelyne tetraamine, a tetradentate ligand $\left(\mathrm{trien}\right)$

EDTA is a hexadentate ligand.